I spoke too soon. I am now seeing pointer freezes on the amd64 machine. Different phenomena, but perhaps associated. I need to switch to a pseudo terminal and "rmmod psmouse; modprobe psmouse" to get control of the pointer back under X. gpm was still working in the pseudo terminal before the reload. Again, this has only started happening recently, so some sort of bug has been introduced in the last month (testing, December 2014).