I create empty project, and do Smart UV project on simple cube. After this, it is possible to select faces in the UV Editor tab ("View") mode:
But when I want to switch to the ("Paint") mode, the selection is reset and brush fill fills the whole image.
I tried to switch to the texture paint mode and enable buttons like "face selection masking for painting" and "Keep UV and edit mode mesh selection in sync", but nothing helps.
My main goal is to be able to fill faces with brush selecting faces in the UV editor mode. Please tell me if this is possible at all.