valid users = @DOMAIN+somegroup doesn't work strangly valid users = @somegroup (somegroup == ADS group name) works. Same is true for write list. I'm using 3.0.23a sernet rpm's. By the way I don't use 'winbind use default domain'. Is this behaviour by design or is it a bug? It clearly changed between 3.0.21c and 3.0.23a.
Confirmed. lookup_name()appears to not honuor the winbind separator but rather assumes a '\'. Change your config to use valid users = @"DOMAIN\name with spaces". for a temporary workaround until 3.0.23b.
fixed in 3.0.23b