Getting PCR amplification at annealing higher than Tm!
It is very common to get annealing at higher than predicted Tm.  If it's a problem in your case, especially if you're getting mis-annealing at lower temperatures, consider using touchdown PCR to find an optimal temperature.  Or, pragmatically, if you have any flexibility in primer design, simply order a set of primers and try them all.  Primers are cheap today, and you'll often find a set that work even where the design programs claim they won't.