Kevin,
I'm still groping around in the dark here, but...
When I leave the mouse enabled, I get no handle_74 messages, even when I wiggle the mouse. I get handle_09 (keyboard) messages, and it fails earlier when I press lots of keys. When that happens I get a buffer full in inhibit instead of enable.
So I'm wondering why handle_74 never gets called. I don't see anything obvious. I tried to get handle_74 messages from qemu, and didn't see them there either. I'm hoping that this is at least part of the problem.
Thanks, Myles