I just saw a comment like this in a piece of code written long ago:
“Do this particular thing because it behaves like this. Not sure why.”
That, to me, is a code smell. If you aren’t sure why a particular piece of code is behaving the way it is, it’s best to take the time to understand why it is behaving the way it is, rather than compensating for it in other places. Compensating for unknown behaviour leads to messy code and unexpected bugs. It makes maintenance harder, because you then have to update code in more than one place. Duplicate code = duplicate bugs = more maintenance = it takes you longer to get new features in.
If you aren’t sure why – learn why! An hour spent now saves ten hours spent later.