I backed Samba out to version 1.9.15p4 (which is the 1.1.x stable package) and this bug went away. Hopefully someone with a lot more experience than I with network code can track down and squish this, I assume it happens to other people as well. I'm pretty sure it is was caused by an attempt to access a non-existant share (was there and then removed when the files moved to a different machine).