Actually, a motor is not a "constant power" device. The power rating for motors is the limit, not a constant.
Inductive reactance aside (to oversimplify to remain in the scope of this discussion), consider a motor like a static resistor. Amps=Volts/Resistance. So, more V = more A for a given R.
Yes, there is a limit to how much power any motor can dissipate. If exceeded, the result is melted coils.
I learn something new everyday. Tahnks for the quick lesson Brian, should keep me straight till I dethink something again. BTW thanks for the emoli cells. I made some nice 5s packs and hope to get my align 600xl powered lsp rolling this weekend.