The validator works, as supposed, my logic have failed:
CCompareValidator, throws an error, when two compared values are not equal. On the other hand, if they're equal -- it passes validation without errors. That is supposed behavior.
I wanted an error, when values are equal (which means, that user is attempting to edit himself or herself) and pass as validated, when both values are different (logged user edits different one).
That's why I need to use
'operator'=>'!=' as configuration of validator. This is the answer.
BTW: All the glory of solving this problem goes to Keith at YiiFramework.com's forum.