Spamassassin & user_prefs configuration

I've a strange problem when I use Usermin gui to set Spamassassin Mail Filter. Web interface work only to write once in user_prefs. After "Save" action I see (in shell) user_prefs file updated with new instructions but Usermin gui is clean like anything saved. I can setup Spamassassin correctly and see changes in gui with virtual server owner or system administrator user from Virtualmin but not with mail user from Usermin...

Any suggestion?

Thanks