What is up with that?
textex, the short story is that this is part of system of checks and balances, and that you'll not be charged for clicks that are over your budget, over time. Clicks that are over your budget, over time, will amount to free advertising for you.
More detailed info is here, from the AdWords Help Center:
Why am I being charged for more than my daily budget on some days?
[adwords.google.com...]
AWA