In my first job out of school, I was writing driver code in C. In one of my projects, I had a code block that wasn't working, but all it did was a switch on ints. On a hunch, I tried ifs, and it worked. Turns out I found a bug in the in-house GCC fork. I'm sure my manager thought I was an idiot--I was a new grad saying my project isn't working, and I think it's a compiler bug.