samba - Mar 2015 - the windows xp clients do not automatically synchronize their time against DC

Hello list
Why my windowsxp clients do not *automatically* synchronize their time
against DC Samba4?.
If I run this command on the client *net time \\ nombre_DC / set /
yes*, the pcs update their  time but if I change the date on the DC,
but if I change date on the DC , computers don't do it.
I will appreciate any help you can give me
Best regards
Dania