...I find that it's actually a feature of Paint Shop Pro, not a bug.
Who'd have thought eh?
Try disabling the Scratchdisk. File> Preferences> General Program Preferences> Display and Caching tab. Uncheck Enable scratch disk.
Might work, might not.
You may find this interesting as you have a 64 bit computer with well over 4gb of RAM. viewtopic.php?p=234089#p234089
This would also likely help on earlier versions of PSP.