I do not know if this is an issue pre-patch or post-patch.
I also do not know if this is an expected consequence of the filter contrast layer as I have not noticed this until now.
Basically, any mask that has some gradience to it will gradient riggidly in a very obvious manner. Especially if done in small scales (The riggid effect becomes noticable) and between contrasting colours (Easier to see). I know that the gradience of the mask tools are actually riggid but in very small subtle ways. Filter Contrast just blows it up.
Up to you guys to make the verdict.
LEVELS filter layer does something similar.
That is a Radial gradient that eases out, inputGamma makes it pretty solid. Again, I do not know if this is intended or not since these are pretty advanced layers to make work right.