The strange thing is that the problem appears only on Windows 8 and 8.1 machines. Windows XP and 7 users doesn't notice any problem.
It looks like this is a samba error: https://bugzilla.samba.org/show_bug.cgi?id=10415
It is filed in the zentyal bug tracker too: https://tracker.zentyal.org/issues/243
Redmond Herrings when they say the co-operate probably.
PS +1 As yeap looks like win 8 causes crashes
http://en.wikipedia.org/wiki/European_Union_Microsoft_competition_caseM$ being M$ try to escape this and when it comes to client advise I would employ M$ technologies that roll up to 2008.
Obviously something is different in Win8 and the poor Samba guys will prob have to reverse engineer the solution.
Or say sod it Ok Win 8 die.
Works with 7, Win 8 just say no!
Samba4 is a Win2008 server, well 2003 that you can elevate any one tried that?
https://wiki.samba.org/index.php/Samba-tool-externalsamba-tool domain level raise --domain-level=2008_R2
samba-tool domain level raise --forest-level=2008_R2
I have doubts it will do much, prob smb3 functionality and maybe we don't use a btrfs backend. Dunno really but maybe a try.