MyISAM index corruption

[Alexey Polyakov]

I have a webserver running a few websites. During last two days, indexes in my databases often became corrupt. I get errors like this in error log:
050804 15:40:41 [ERROR] /usr/local/libexec/mysqld: Can't open file: 'rasstext.MYI' (errno: 145)

There are 36 databases (including mysql), total size of data/index files is only about 150 megs.
OS I use is FreeBSD 5.4 Release. Mysql version is 4.1.12, installed from port, with linuxthreads support.
I couldn't find any pattern in those errors - looks like that random tables that get inserted into have their indexes corrupted.

First I thought that delayed key writes may cause this - turning them off didn't help. Also I tried setting table cache size to very small value, so server closes/opens table files almost any time it needs to access them. Didn't help either.

mysqld never crashed. Table indexes get repaired on the fly (I have myisam_recover = BACKUP,FORCE), though I lost some records when repairing one of the tables:
050804 4:26:01 [ERROR] /usr/local/libexec/mysqld: Can't open file: 'banner_adstats.MYI' (errno: 145)
050804 4:26:01 [Warning] Checking table: './jewelry/banner_adstats'
050804 4:26:01 [Warning] Recovering table: './jewelry/banner_adstats'
050804 4:26:01 [Note] Retrying repair of: './jewelry/banner_adstats' with keycache
050804 4:26:02 [Note] Found 3663 of 3674 rows when repairing './jewelry/banner_adstats'

So, my questions are:
What should I do to determine what is causing problems and give a better report?
Is switching to InnoDB until this bug gets found and fixed a good idea?

Thanks.
Alexey