* The mask was not subdivided properly on splitting edges, which gave interesting
but definitely wrong fractal-like borders around masks.
* Edge splitting was only done where the mask was < 50%, with the reasoning that
you can't do a 50% topology update. But this gives an ugly border in the mesh.
The mask should already make the brush move the vertices only 50%, which means
that topology updates will also happen less frequent, that should be enough.
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