Samba 3.0.23c running on IBM AIX in an LPAR environment. Affected clients are running OS X.4 (Tiger).
Always reproducible in OS X, problem doesn't appear on Linux or Windows clients attaching to the same shares.
Very similar to (if not the same as) the bug outlined here: https://bugzilla.samba.org/show_bug.cgi?id=3819
One of your I think James :-).
This is a OSX client bug, please report to Apple.