I was ICQing with Tony on this one, and I think it's related to this:

"I'm guessing that the kernel code drops the display so quickly that the amp looses power in a similar way to the Mk1s. I doubt they would be able to fix it properly in software, and keep the low power code as nice as it is."

This is just based off my observations from looking at the empeg_power.c file in the kernel.