I have since upgraded to 1.1b8 but this morning my attention was called to this error from 1.1b7:

Nov 11 06:35:17 hill dovecot: IMAP(voice): file mail-cache-lookup.c: line 68: unreached Nov 11 06:35:17 hill dovecot: child 70673 (imap) killed with signal 6 Nov 11 06:35:17 hill dovecot: IMAP(voice): Connection closed bytes=262/25869

I can't say for sure but it was probably a squirrelmail connection. It wasn't me, and I wasn't even awake at the time so I don't know how to reproduce it.