Adding a comment sometimes caused compile failure
This is going back 30+ years when 1MB was a large machine.
Someone added a comment to some code, compiled it successfully, and submitted it to be integrated. This compile failed with a syntax error. Because it "broke the build" there was an investigation.
The team leader spoke to the junior programmer and stressed the need to compile before integrating. "I did compile it" said the trog*. Team leader said "ok we'll compile it again and show it fails" "oh it works - hey Charlie... here's an interesting problem..." and so on up the chain"
It turns out that when the original program was compiled, the source would fit in memory. When the comment was added, it was too large for memory, and so used "the spill file". This had a bug where it missed a byte when reading from the spill file - and put a garbage byte in the line.
* trog - troglodyte: in pre-historic times, someone who lived in a cave.