actually I wonder how field User Groups works, looks like values are stored as 1,2,3...etc. But when I create checkbox field it should also store values like 1,2,3...
I tried to set multiple usergroups by creating checkbox field and use Conditional States to fill standard Usergroups field. And this solution doesn't work seems...or I do something wrong??
Yes I did mistake! to let users select multi groups I must remove default group in General settings of Joomla 3!