It's been ok for me (Score 4, Interesting)

A few years ago I was renewing my car tabs on the WA state's site and they had a box for 'donations to DOT' or somesuch. For kicks I tried putting in a negative value, and sure enough it reflected the total for my tabs as less. I went ahead and submitted things with a dollar taken off the value, just to see if it would actually go through. Sure enough, a week later I received my tabs, and the mathematically correct but embarrassing negative donation on my receipt.

I ended up calling them and letting them know about the bug. They were nice about it, and the next year at least it was fixed.

-Nic