Fabulous software (mac 1.6.7) so this isn't a moan - just an observation (and irritation if I'm honest!)
The selection brush and the refine feature are much, much better that PS.
However when I create a masked cut-out and then place it in another layout, unexpected edge lines are appearing ( see screenshot attached)
If I go back to the original image and paint over these unexpected edges on the mask (note I can't see them on the mask) - I just paint where I assume the error to be. I then save the cutout and place it again in the AP layout. (I am looking forward to you getting linking sorted out).
However the errors are still present. Baffled!
The only solution I have is the crop the cut-out by 1 or 2 pixels. This solves the problem however it is not ideal.
Anyone got any thoughts on this? Is it a bug or a feature?