s this happening with one specific image, or all images?
How big is the image, and what is it's bit depth?
I realize you are discounting scratch space, but if it is not RAM, I'd look more closely and scratch. What size are the Photoshop temp**** files in the root directory of your primary scratch drive? Do you have any orphaned Photoshop temp*** files with old dates clogging up scratch space?
If it is one particular image, a trick that can fix things when a file goes weird on you is to group all the layers, and duplicate to a new document. Note, that while this transports alpha channels, you would lose and work paths.
Something else that occurs to me, what is the brush size you are using with the Spot Healing brush?
Duplicating to a new document worked. Thanks Trevor!
OK, that's cool. I don't know if you had any work paths in the original. Like I said, you can't directly drag or copy to the new document, but if you:
- Select the work path in the original and copy with Ctrl c (Cmd c)
- Switch to the new document and make a new work path and paste with Ctrl v (Cmd v)
That will do the trick. Or you can make all work paths into shape layers before duplicating. There is probably a more elegant way of copying work paths between document though. (Hmmm I just searched and didn't find one.)