I am referring to this thread
https://irfanview-forum.de/showthread.php?t=10129
as the offending bug is obviously not solved and I would like to contribute some info, however, the thread is closed, so I put it here:

I experienced the same bug when using the Paint plugin initiated by pressing F12:
  1. Start Irfan View
  2. paste a screenshot from clipboard
  3. press F12
  4. activate "draw rectangle" or "fill"
  5. execute the desired action

--> Irfan View freezes and is not usable any more

I use Win7 x64 Home Premium on an INTEL i3 2120 with 8 GB RAM and 4 cores ( incl. hyperthreading). I have version 4.51 x64 incl. all plugins installed, ticking the checkbox "for all users" while installing.

When I repeatedly ran into this behaviour I first saved the image and then started the Paint plugin. This worked a couple of times. After those times were over, saving first didn't make a difference. However, after running 4.51 x64 with admin privileges no crash occurred. As I can't save into my ususal "My Images"-folder when running with admin rights I installed x86 version 4.51 incl. Plugins. My OS informed me afterwards that the installation was probably not performed correctly and whether I wanted to try to reinstall. I declined this at both instances for Irfan View and the plugins. Now it seems to be fine with x86 installation...so far...

Just thought I'd share the info, as I've become really reliant on IrfanView and use it for both private and business (which my employer paid for).