Strange Heatbed temp fluctuation

I have an M505 Prusa that came with the standard heatbed with aluminum plate, and when I try to set the heatbed temp to 95, I notice the temp will rise to 82c and then periodically jump to 95 for a split second and then back to 82c. Could it be a bad thermister? It only does this with temps above 82. I think the bed is heating up to 95, but I'm not getting the correct reading.

Try a different firmware, e.g. Repetier. If it doesn't work, get a new thermistor (and switch back to Marlin if you want). If it does, it's in software.

It could be the thermistor table used has an error. If it's one of the included ones, download a fresh copy of Marlin.

I may have to upgrade the firmware, only I've heard people have trouble getting the LCD working. The board I have is a cloned Melzi, which has no documentation for it.

See this photo. I have my bed temp set to 90, but it reads 97. It only does this with temps above 82c. Very strange behavior. Do think it has something to do with the PID tuning?