Problem with planner

Hi,
we have 8.3.11 installation on client site, with table, which looks like
this:

$ \d objects
Table "public.objects"
Column | Type | Modifiers
-------------------------+--------------------------+---------------------------------------------------------------
...
state | text |
...
ending_tsz | timestamp with time zone | default (now() + '4 mons'::interval)
...
Indexes:
"objects_stat_user_id_creation_tsz" btree (state, user_id, creation_tsz)
"objects_ending_tsz_active" btree (ending_tsz) WHERE state = 'active'::text
"objects_ending_tsz_idx" btree (ending_tsz)
...

and we have a query:
select count(*) from objects where state='active'::text and ending_tsz <= ( select now() - '1 day'::interval );

Normally this query has been getting plan, using
objects_ending_tsz_active, which is sane and fast.

But today, without any sensible reason, it switched to:

QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=6719810.62..6719810.63 rows=1 width=0)
InitPlan
-> Result (cost=0.00..0.01 rows=1 width=0)
-> Bitmap Heap Scan on objects (cost=1289719.58..6711422.56 rows=3355219 width=0)
Recheck Cond: ((state = 'active'::text) AND (ending_tsz <= $0))
-> BitmapAnd (cost=1289719.58..1289719.58 rows=3355219 width=0)
-> Bitmap Index Scan on objects_stat_user_id_creation_tsz (cost=0.00..334318.95 rows=10065657 width=0)
Index Cond: (state = 'active'::text)
-> Bitmap Index Scan on objects_ending_tsz_idx (cost=0.00..953722.77 rows=24986738 width=0)
Index Cond: (ending_tsz <= $0)
(10 rows)

running analyze objects 2 times in a row fixed the issue, but hour later
- the problem came back.

what can be wrong?

Best regards,

depesz

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