It seems that the PCI subsystem notices that all irq sources
share irq 9 and reroutes interrupts.
But after rerouting the interrupts it notices that something
is wrong and aborts the irq change, without undoing the
rerouting.

Thus the usb controller waits on irq 9, and doesn't receive
the interrupts.
If you play sound, you effectively poll the irq handler of
the USB controller, and then you can use your mouse.

Could you apply the attached patch, reboot and post the dmesg
output? And append cat /proc/interrupts.

--
	Manfred