The entire part of emit() which sends to the socket is wrapped in an except: which should catch all except KeyboardInterrupt and SystemExit. The except clause calls the handleError method of the handler. See

http://hg.python.org/cpython/file/fa277cbd66bb/Lib/logging/handlers.py#l804

So I can't see exactly what's happening, and moreover I can't reproduce this on Linux even when sending messages of > 16384 on the Unix socket. I don't have access to a FreeBSD system.

Can you do a little more investigation, since I'm not sure what your source says? (The line nos. don't seem to match up exactly - in Mercurial, line 808 is an except socket.error clause).