Paint Shop Pro Exit Weirdness

[Enjay]

Nothing to do with GZDoom.

I use Paint Shop Pro 7.04 as my go-to pixel editing tool. I use it several times a day and have done for years. However, the program is old and I have started experiencing a problem that *might* be related to that and compatibility with the current windows build. I know that a few other people also use PSP, so I was wondering if anyone else was experiencing something similar and perhaps might even have a solution?

What happens:
PSP is set as my default program for many graphics types. If I double-click on one of the associated files, PSP opens with the file loaded (i.e. normal behaviour).

However, recently, if I do that, if I then close PSP, my computer is clearly doing something that keeps it busy for a few seconds (I dunno, releasing memory or something). Often I get the little animated circle beside the mouse pointer and Windows explorer is slow to respond.

Typical scenario:
I have a folder full of texture or sprite images.
I double-click one to open it.
I close PSP.
I try to click the next image in the folder but my computer is busy and I cannot click/select/whatever the next picture.
After a few seconds, my computer becomes responsive again.

The above will also happen if I am trying to do the above but from inside, say, a 7zip window with a zip file open.

Other programs (such as Paint.net) do not exhibit this problem.

I have tried uninstalling PSP and reinstalling it - no improvement.

I have tried various compatibility mode settings - nothing improved the situation.

Anyone got any ideas?

[Edit] Oh, I meant to say, the problem only seems to happen when follwing the above steps (which, unfortunately, is how I tend to use it). If I open PSP first, then drag and drop a file onto the open window, then close the window, I don't seem to get the problem. i.e. it only seems to happen when opening a file from explorer by double-clicking (or right-click "Open with...").