I'm also experiencing the same problem on a dual processor Sun v20z.
For me, disabling the bootup splash screen solved the problems. (I've removed
'splash' from 'nonaltoptions' in /boot/grub/menu.lst and ran update-grub.)
So IMHO vga16fb is the problem, or at least that's what seems to trigger the
problem.
I'm also experiencing the same problem on a dual processor Sun v20z.
For me, disabling the bootup splash screen solved the problems. (I've removed
'splash' from 'nonaltoptions' in /boot/grub/menu.lst and ran update-grub.)
So IMHO vga16fb is the problem, or at least that's what seems to trigger the
problem.