This is a pretty random Notepad story, but: in 1999 I was doing web development for Internet Explorer 6 (yes, I know) using Classic ASP and Visual Basic (5 or 6? I can't be bothered to look shit like that up). Probably my most important debugging tool was the "View Source" menu option in IE6, which would bring up the raw HTML of whatever page I was working on in Notepad. One day the "View Source" option just stopped working, completely. Clicking that menu wouldn't do anything at all; I tried everything I could think of but just couldn't fix the problem. For six months I was basically coding blind - I had no way of directly seeing the HTML my code was producing.
Somehow I managed to still get my work done. Then one day I stumbled across an obscure forum post that said "View Source" in IE6 would not work if you had a shortcut to Notepad on your Desktop. I of course had a shortcut to Notepad on my Desktop since I kept everything on my desktop (yes, I know). I renamed my shortcut to "NotepadX" and suddenly "View Source" in IE6 started working again. Possibly the happiest day of my programming life. I played around with it and found that it didn't have to actually be a shortcut to Notepad - it could be a shortcut to any program or file, but if it happened to be named "Notepad" it would block View Source from working.
I would give anything to find out where this particular bug came from. It's really bothered the shit out of me for the past 26 years. I don't see how it could ever happen accidentally, so I have to assume that some MS programmer somewhere really hated people with shortcuts to commonly-used programs on their Desktop and decided to punish them.