strange file-permission problem

[Mikhail Teterin]

Hello!

I've encountered a problem, which went ahead most of the things I know about 
Unix file permissions:

 dovecot at bonkers:run/dovecot/login (10) ls -l ssl-parameters.dat
 -rw-r-----  2 root  dovecot  230 Apr 13 00:33 ssl-parameters.dat
 dovecot at bonkers:run/dovecot/login (11) groups
 dovecot
 dovecot at bonkers:run/dovecot/login (12) id
 uid=143(dovecot) gid=9005(dovecot) groups=9005(dovecot)
 dovecot at bonkers:run/dovecot/login (13) cat ssl-parameters.dat > /dev/null
 cat: ssl-parameters.dat: Permission denied
 dovecot at bonkers:run/dovecot/login (14) ls -ld
 drwxr-x---  2 root  dovecot  512 Apr 15 14:44 .

I had to set the mode of ssl-parameters.dat to 644 to allow dovecot-users to 
login, but it should not be needed -- the file should be readable by members 
of the group "dovecot" (such as user "dovecot").

And yet, when the user dovecot tried to open it, it got EPERM.

Could somebody, please, explain? Thanks!

 -mi