"It's not everyday you come across this."

Ugh, it's more common than you want to know, and you should check if there is any similar carryover mistake for retirement, HSA, too. Anything wage or annually limited, in other words.

You might not see this very often, because someone like me goes in there and straightens it out before year end, if you're lucky. Or the new staff shows up in my payroll class and all is revealed as we learn.