Why is turbotax online adding an estimated tax penalty (1040, line 24) when I'm paying 110% of last years taxes?

[SteamTrain]

Depends on how it was paid...if the 110% was reached unevenly, with uneven, or fewer than 4 quarterly estimated tax payments, then a penalty may still be involved unless you work thru the form 2010AI annualized Income form, breaking everything up by "quarters"  (3mo, 2mo, 3mo, 4mo) .   

I wouldn't bother if the penalty was under $100 though....the 2010AI is a real pain to fill out.