ERR msearch_stats_db[4515]: mserver5: gdk_batop.c:175: insert_string_bat: Assertion `v >= ((var_t) (((1<<10) * sizeof(stridx_t)) >> 0))' failed.

I see above error in merovingian.log while performing a specific select query and the client says "Connection terminated":
select id, col2, col3, col4, col5, timestamp, count(*) from stats_daily where id=38 group by "id", "col2", "col3", "col4", "timestamp", "col5" having count(*) >1;
There's a unique key on the table stats_daily on (id,col2,col3, col4, timestamp, col5).
However following query succeeds(it just has more selection conditions):
select id, col2, col3, col4, col5, timestamp, count(*) from stats_daily where  col2 <> '' and col3  <> '' and col4  <> '' and col5  <> '' and id  <> 0  group by "id", "col2", "col3", "col4", "timestamp", "col5" having count(*) >1;

One thing I know for sure is that there was an error in inserting records into the DB at some point before:
Following is an excerpt from the merovingian logs:
2013-01-10 10:40:49 ERR msearch_stats_db[19210]: !mal_mapi.listen: expected filedescriptor, but received something else
2013-01-10 10:40:57 ERR merovingian[8996]: client error: client [XX.XX.XX.XX]:51573 sent challenge in incomplete block:
2013-01-10 10:45:29 ERR msearch_stats_db[19210]: mserver5: bat_storage.c:40: delta_bind_del: Assertion `b' failed.
2013-01-10 10:45:29 ERR msearch_stats_db[19210]: mserver5: bat_storage.c:40: delta_bind_del: Assertion `b' failed.
2013-01-10 23:48:18 ERR msearch_stats_db[31637]: !mal_mapi.listen: expected filedescriptor, but received something else
2013-01-10 23:48:19 ERR msearch_stats_db[31637]: !mal_mapi.listen: expected filedescriptor, but received something else
2013-01-10 23:48:32 ERR msearch_stats_db[31637]: !FATAL: BBPdir: subcommit attempted without backup BBP.dir.
2013-01-11 04:29:31 ERR msearch_stats_db[4480]: mserver5: gdk_batop.c:175: insert_string_bat: Assertion `v >= ((var_t) (((1<<10) * sizeof(stridx_t)) >> 0))' failed.

Also,
I keep getting "!mal_mapi.listen: expected filedescriptor, but received something else" almost every second(Performing continuous inserts into the db).
Also attaching a subset of mervingian log that may contain other kinds of ERR s than above.
What other diagnostics can I do?
PS: Running on Feb2013 branch. changeset:   38061:d1a99a110b63
Ubuntu 12.10 64 bit.

Regards,
Tapomay.