When I compare two text files with Notepad++ 5.8.2 Compare Plugin 22.214.171.124 on my Windows 7 64-bit system, the result is a repeated flashing screen.
The only way out is to force a system shutdown via Ctrl-Alt-Del. Even this is not easy, if you have any unsaved files.
It would seem that the fact my system is the 64-bit version of Windows 7 may be the significant circumstance here.
The symptom does not occur on the 32-bit version of Windows 7.
I have copied this from http://ehc.ac/p/notepad-plus/bugs/3002/ and put it here which seemed like a more official place for it..