God, that's odd.
There's these fucky hit circle overlays scattered about the slider. See picture:

Any fix for this? It seems if I make the hitcircleoverlay file the same size as the hit circle in the skin, it fixes it...
EDIT:
More research leads me to believe the anchor point for hitcircleoverlay is not at the center of the image but at a constant point (x,y) for sliders only.
EDIT2:
On a lighter background, it appears there is black at the edges? This is suggestive of a couple different things... my guess is that it is taking the transparency value at that point and turning it black. I would also venture to guess that there is clipping based on the hit circle size for some odd reason.


EDIT3:
Isn't it just far easier to set the center of an image as the anchor point, then set where that image has to spawn as a point in the editor? Center can be found by halving the dimensions of the image and setting them as coordinates (256x128 -> 128,64 is the center). I'm pretty sure that's more than possible. It would solve the hit circle size needing to be a certain size and solve problems regarding this hit circle overlay. Balancewise, just resize hit circle if it is too big.