Server OES2Sp2 with GW8.0.2hp3.
All partitions - ext3.

At check often I find errors of a look:
STRUCTURAL VERIFICATION of database /gwsystem/kujbd/gwkujbp/ofuser/usernyy.db
Verifying data
- database updated since processing began; resyncing check
- structural problem detected- BAD_BLK_HDR_TYPE (code 0x32 )
- Additional info saved in /gwsystem/kujbd/gwkujbp/ofuser/usernyy.$er
Problem 13- Structural problem found in database /gwsystem/kujbd/gwkujbp/ofuser/usernyy.db
- Attempting to correct structural problem in database
- Beginning rebuild for database usernyy.db
Saving old database to backup usernyy.dba
Writing corrected records back to database
- Rebuild succeeded

Mistake of this kind at different users.
for example - today at users: u23, u34, and the day before yesterday u45 had u1, u21, u17.
Sometimes such error happens in several msg??.db.

The post office didn't crush, no failures on the server are present.

From where this mistake arises?
What to make, that such mistake wasn't?