[hermitdev]

> I really don't know how you can actually make a pothole worse by attempting to fix it.

My first thought would be using substandard or incorrect materials. Say, using concrete in an asphalt surface. You quasi cover this with your cardboard part of the comment. Perhaps an incorrect mix of aggregate to asphalt might have different thermal properties. If the pothole expanded more/faster than the surrounding material, it might make it a lot worse. Also, if your materials are not safe to drive on while setting (like my example, filling a hole with concrete). You'd also be endangering yourself and others while attempting such work as you'll be unsuitably marked and lanes won't be properly barricaded for your work.