Initially it looks like:

After swiping over his face using the deform move tool:

AAAAAHHH

The layer is set to normal, and so is the tool's blending mode. I didn't touch the settings and it worked perfectly earlier.
I already tried restarting Krita and my PC. Help?

( Duplicate of this post: viewtopic.php?f=139&t=141078 )

Did you try to set the brushes's blending mode to copy?

That looks similar to when the alpha channel is locked, either on the layer or on the brush, note that for the brush is not on the settings but rather on the toolbar, the little checkered square button called "preserve alpha", this one doesn't deactivate even after resetting the brush settings, is manual. This is just a guess though.