diff -r 941608f8b3fb src/lib-mail/istream-header-filter.c
--- a/src/lib-mail/istream-header-filter.c	Tue Jun 01 16:01:21 2010 +0100
+++ b/src/lib-mail/istream-header-filter.c	Tue Jun 01 16:07:48 2010 +0100
@@ -63,6 +63,7 @@
 		return -1;
 	}
 
+	i_debug("%p: hdr-filter read mixed", &mstream->istream.istream);
 	data = i_stream_get_data(mstream->istream.parent, &pos);
 	if (pos == body_highwater_size) {
 		ret = i_stream_read(mstream->istream.parent);
@@ -282,6 +283,7 @@
 
 	if (!mstream->header_read ||
 	    stream->istream.v_offset < mstream->header_size.virtual_size) {
+		i_debug("%p: hdr-filter read header offset=%lu", &stream->istream, (long)stream->istream.v_offset);
 		ret = read_header(mstream);
 		if (ret != -2 || stream->pos != stream->skip)
 			return ret;
@@ -295,6 +297,7 @@
 	v_offset = stream->parent_start_offset + stream->istream.v_offset -
 		mstream->header_size.virtual_size +
 		mstream->header_size.physical_size;
+	i_debug("%p: hdr-filter read body at %lu", &stream->istream, (long)v_offset);
 	i_stream_seek(stream->parent, v_offset);
 	return i_stream_read_copy_from_parent(&stream->istream);
 }
@@ -303,6 +306,7 @@
 i_stream_header_filter_seek_to_header(struct header_filter_istream *mstream,
 				      uoff_t v_offset)
 {
+	i_debug("%p: hdr-filter seek-to-header", &mstream->istream.istream);
 	i_stream_seek(mstream->istream.parent,
 		      mstream->istream.parent_start_offset);
 	mstream->istream.parent_expected_offset =
@@ -328,9 +332,11 @@
 	if (mstream->istream.access_counter !=
 	    mstream->istream.parent->real_stream->access_counter) {
 		/* need to re-parse headers */
+		i_debug("%p: hdr-filter access reset", &mstream->istream.istream);
 		i_stream_header_filter_seek_to_header(mstream, 0);
 	}
 
+	i_debug("hdr-filter skip header");
 	while (!mstream->header_read &&
 	       i_stream_read(&mstream->istream.istream) != -1) {
 		(void)i_stream_get_data(&mstream->istream.istream, &pos);
@@ -353,6 +359,7 @@
 	struct header_filter_istream *mstream =
 		(struct header_filter_istream *)stream;
 
+	i_debug("%p: hdr-filter seek %lu to %lu", &stream->istream, (long)stream->istream.v_offset, (long)v_offset);
 	if (stream->istream.v_offset == v_offset) {
 		/* just reset the input buffer */
 		stream_reset_to(mstream, v_offset);
@@ -360,11 +367,11 @@
 			      mstream->istream.parent_expected_offset);
 		return;
 	}
-
 	if (v_offset == 0) {
 		/* seeking to beginning of headers. */
 		stream_reset_to(mstream, 0);
 		i_stream_header_filter_seek_to_header(mstream, 0);
+		i_debug("%p: hdr-filter /seek", &stream->istream);
 		return;
 	}
 
@@ -385,6 +392,7 @@
 		i_stream_seek(stream->parent,
 			      stream->parent_start_offset + v_offset);
 	}
+	i_debug("%p: hdr-filter /seek", &stream->istream);
 }
 
 static void ATTR_NORETURN
@@ -401,6 +409,7 @@
 	const struct stat *st;
 	uoff_t old_offset;
 
+	i_debug("%p: hdr-filter stat", &stream->istream);
 	st = i_stream_stat(stream->parent, exact);
 	if (st == NULL || st->st_size == -1 || !exact)
 		return st;
diff -r 941608f8b3fb src/lib/istream-file.c
--- a/src/lib/istream-file.c	Tue Jun 01 16:01:21 2010 +0100
+++ b/src/lib/istream-file.c	Tue Jun 01 16:07:48 2010 +0100
@@ -106,7 +106,7 @@
 
 	if (!stream->istream.seekable) {
 		if (v_offset < stream->istream.v_offset)
-			i_panic("stream doesn't support seeking backwards");
+			i_panic("%p: stream doesn't support seeking backwards", &stream->istream);
 		fstream->skip_left += v_offset - stream->istream.v_offset;
 	}
 
@@ -165,5 +165,6 @@
 	}
 	fstream->istream.istream.readable_fd = TRUE;
 
+	i_debug("%p: create file", fstream);
 	return i_stream_create(&fstream->istream, NULL, fd);
 }
diff -r 941608f8b3fb src/lib/istream-limit.c
--- a/src/lib/istream-limit.c	Tue Jun 01 16:01:21 2010 +0100
+++ b/src/lib/istream-limit.c	Tue Jun 01 16:07:48 2010 +0100
@@ -37,6 +37,8 @@
 		return -1;
 	}
 
+	i_debug("%p: limit read, seeking parent=%p to=%lu", &stream->istream, stream->parent, 
+		(long)(lstream->istream.parent_start_offset + stream->istream.v_offset));
 	i_stream_seek(stream->parent, lstream->istream.parent_start_offset +
 		      stream->istream.v_offset);
 
diff -r 941608f8b3fb src/lib/istream-tee.c
--- a/src/lib/istream-tee.c	Tue Jun 01 16:01:21 2010 +0100
+++ b/src/lib/istream-tee.c	Tue Jun 01 16:07:48 2010 +0100
@@ -219,6 +219,7 @@
 	tstream->next = tee->children;
 	tee->children = tstream;
 
+	i_debug("%p: create tee child", tstream);
 	ret = i_stream_create(&tstream->istream, input, i_stream_get_fd(input));
 	/* we keep the reference in tee stream, no need for extra references */
 	i_stream_unref(&input);
diff -r 941608f8b3fb src/lib/istream.c
--- a/src/lib/istream.c	Tue Jun 01 16:01:21 2010 +0100
+++ b/src/lib/istream.c	Tue Jun 01 16:07:48 2010 +0100
@@ -9,6 +9,7 @@
 {
 	i_free(stream->real_stream->iostream.name);
 	stream->real_stream->iostream.name = i_strdup(name);
+	i_debug("%p: name=%s", stream, name);
 }
 
 const char *i_stream_get_name(struct istream *stream)
@@ -37,6 +38,7 @@
 	struct istream_private *_stream = (*stream)->real_stream;
 
 	if (_stream->iostream.refcount == 1) {
+		i_debug("%p: freed", stream);
 		if (_stream->line_str != NULL)
 			str_free(&_stream->line_str);
 	}
@@ -108,11 +110,16 @@
 	stream->eof = FALSE;
 	stream->stream_errno = 0;
 
-	if (_stream->parent != NULL)
+	i_debug("%p: read offset=%"PRIuUOFF_T, stream, stream->v_offset);
+	if (_stream->parent != NULL) {
+		i_debug("%p: seeking parent=%p offset=%"PRIuUOFF_T, stream,
+			_stream->parent, _stream->parent_expected_offset);
 		i_stream_seek(_stream->parent, _stream->parent_expected_offset);
+	}
 
 	old_size = _stream->pos - _stream->skip;
 	ret = _stream->read(_stream);
+	i_debug("%p: read ret=%d", stream, (int)ret);
 	switch (ret) {
 	case -2:
 		i_assert(_stream->skip != _stream->pos);
@@ -179,11 +186,20 @@
 	data_size = _stream->pos - _stream->skip;
 	if (count <= data_size) {
 		/* within buffer */
+		i_debug("%p: skip: %lu + %u = %lu", stream,
+			(long)stream->v_offset, (int)count,
+			(long)(stream->v_offset + count));
+
 		stream->v_offset += count;
 		_stream->skip += count;
 		return;
 	}
 
+	i_debug("%p: skip seeks: %lu + %u = %lu (count=%u <= data_size=%u (skip=%u pos=%u))", stream,
+		(long)stream->v_offset, (int)count,
+		(long)(stream->v_offset + count), (int)count, (int)data_size,
+		(int)_stream->skip, (int)_stream->pos);
+
 	/* have to seek forward */
 	count -= data_size;
 	_stream->skip = _stream->pos;
@@ -214,12 +230,16 @@
 	struct istream_private *_stream = stream->real_stream;
 
 	if (v_offset >= stream->v_offset &&
-	    i_stream_can_optimize_seek(_stream))
+	    i_stream_can_optimize_seek(_stream)) {
+		i_debug("%p: seek: %lu -> skip %u = %lu", stream,
+			(long)stream->v_offset, (int)(v_offset - stream->v_offset),
+			(long)v_offset);
 		i_stream_skip(stream, v_offset - stream->v_offset);
-	else {
+	} else {
 		if (unlikely(stream->closed))
 			return;
 
+		i_debug("%p: seek: %lu -> seek to %"PRIuUOFF_T, stream, (long)stream->v_offset, v_offset);
 		stream->eof = FALSE;
 		_stream->seek(_stream, v_offset, FALSE);
 	}
@@ -536,7 +556,7 @@
 	size_t available;
 
 	if (stream->istream.v_offset > v_offset)
-		i_panic("stream doesn't support seeking backwards");
+		i_panic("%p: stream doesn't support seeking backwards", &stream->istream);
 
 	while (stream->istream.v_offset < v_offset) {
 		(void)i_stream_read(&stream->istream);
@@ -581,6 +601,8 @@
 {
 	_stream->fd = fd;
 	if (parent != NULL) {
+		i_debug("%p: created parent=%p name=%s",
+			&_stream->istream, parent, i_stream_get_name(parent));
 		_stream->access_counter = parent->real_stream->access_counter;
 		_stream->parent = parent;
 		_stream->parent_start_offset = parent->v_offset;
@@ -588,6 +610,8 @@
 		_stream->abs_start_offset = parent->v_offset +
 			parent->real_stream->abs_start_offset;
 		i_stream_ref(parent);
+	} else {
+		i_debug("%p: created parent=NULL", &_stream->istream);
 	}
 	_stream->istream.real_stream = _stream;