Sometimes when I'm drawing, I can see a bit of residue (for lack of a better word) left over from erased or hidden layers.
Here's what it looks like:
http://i66.tinypic.com/90c1g6.png
It is very faint and sometimes I can't see it at all. If you zoom in the image and tilt your head around, you can see shadowy parts of a human body. (This particular screenshot is from a set of human refs.) The most noticeable part is the top right corner.
It isn't connected to any layer or to the background, and it cannot be erased. The layer that these were on was deleted hours ago.
It isn't an issue with my computer, either; it shows up across multiple devices and moves with the drawing, so it isn't burned into the screen or anything.
Does anyone know what causes this or how to fix it? Thanks!