I remember when I learned that command.com kept the current .bat file open when running it, rather than reading it into memory (like most other interpreters that I used or learned at school). We had a client on a Novell network with a menu program that generated .bat files to start the program selected, then restart the menu program. This turned out not to work very well on a multi-user network, as user A would exit an app, and continue running the .bat at some offset, which user B would now have caused to have different content, and probably not even a line break at said offset into "THE" file.

Easy enough to fix by having the menu program put the run script (.bat file) into the Novell equivalent of each user's home directory, but it was a real WTF moment at first :-)