Sounds like a variation on Ayn Rand's "contradictions do not exist, if you think you see one, check your premises, some of them will be wrong".
When we do TimesFive(x) and my answer is 50 instead of the 25. I check the TimesFive function and it's just "print x*5". But how is that possible? 5x5 is 25!
The problem in this case is my assumption that x would be 5 was wrong.
I've had this issue before in my code (though not as trivial an example of course), but it's always a good reminder of something to check when troublshooting.