Had a really weird issue with:

sieveshell localhost

core dump would follow. So I tried to debug this by putting print statements to see what function would fail. That brought me deep into the bowels of Cyrus IMAP and next into Cyrus SASL.

In the end the final function that failed was gss_init_sec_context() which appeared to be a FreeBSD function. And that finally gave me a Google search on the the problem. It's a very long thread, but the solution is here.

Another would be to disable gss.

Not sure if Jeremy Chadwick's patch is already accepted, because, if not, with the next cvsup the problem will come back.