Ah, I think we've seen this before. There's a silly bug in the memory settings control, such that if the only thing you change is the RAM size, and then you immediately close the settings without changing anything else, the change won't be saved. Try changing the memory size and the processor count, then change the processor count back.
I believe this bug has already been addressed in our internal builds of Fusion.
Let us know if that's what you're seeing there!
Cheers,
--
Darius