My guess is that your problem has been resolved upstream, and will be fixed when you have a more recent version of Samba installed. 7.1.3 is almost two years old. It uses Samba 3.0.10, whereas 7.4 uses the much more mature 3.0.28.
EDIT: Confirmed that Vista support was forthcoming at some point after 3.0.14(a). Source - Asianux release notes.