[Dovecot] "Unstable" vs "Development" vs "Nightly"

I'm currently running v2.1rc1, but have been seeing errors like:

Dec 8 11:31:55 it kernel: auth[18914]: segfault at 48 ip 00fe2f74 sp bfcaccd0 error 4 in libauthdb_imap.so[fdd000+f000]

The unstable and nightly builds are newer, but are they likely to be more or less stable than the version I'm currently running?

I'd like to install a newer version, but am trying to get a feel for how usable they're likely to be.

Thanks,

Terry