fts_solr Bad Request / BUG: Unknown internal error

[Nick Rosier]

Hi,

yesterday I created a new mailbox; ever since (and only for the new 
mailbox) I am getting these errors:

2015-06-12T00:00:29.808526+02:00 mail dovecot: 
indexer-worker(xxx at example.com): Error: fts_solr: Lookup failed: Bad 
Request
2015-06-12T00:00:29.808560+02:00 mail dovecot: 
indexer-worker(xxx at example.com): Error: Mailbox INBOX: Status lookup 
failed: BUG: Unknown internal error

Is this a known issue?
Rgds,
N.