Hi!
I think, they use same fabrication process for all AVRs, so it is not as surprising that it works with 32MHz clock. You motivate me to test it at least on spare time.
It is some time ago, but I think Krupski had presented here ATmega2560 at 32MHz. This is only 16MHz MCU according the datasheet.
BTW: The link "www.smartshow.lighting" below your karma is incorrect.