The first time it happened, I had just booted the computer, went in to Pelles C IDE and tried to copy and paste from one source file to another, but the paste function wouldn't work. For more than a day, no matter how I tried to paste, paste wouldn't work, until I set-up to record a screen capture of the problem, at which point paste started working again.
The second time it failed, I had been in Pelles C IDE all day and paste was working fine until it suddenly wasn't.
And as I pointed out earlier, the tool icon shows there is something on the clipboard, and I can paste into WordPad or NotePad, but not Pelles C IDE.