Here’s a couple I didn’t mention earlier
The Autodesk discussion group editor inserts spaces into URLs longer than a certain size (about 70 characters, it seems). It will insert spaces in one place for the URL that it says is displayed on the screen, in another place for the URL that’s actually invoked when clicked, and sometimes in even more places on the URL that really is displayed on the screen. Sometimes the space appears as a space and sometimes it appears as %20. The editor will cunningly allow you to apparently fix up these errors in the places they occur, and then the fun-loving little sprite …