Hey again, just bumping this with what appears to be a related bug.
It's hard to explain, but it seems that the nested mask doesn't work properly when objects are enabled/disabled. I tried to record an example in this clip. The bigger mask is the phone area itself, and the smaller mask is the chat backlog area. If I deactivate the object hierarchy with the chat backlog mask and then re-activate it, the child mask doesn't work and the STM object only responds to the first mask (you can see the text peeking out in between the backlog area and the phone area). Then if I deactivate/reactivate the STM object (or change anything inside of it), it updates/refreshes somehow and then it works properly.