I believe that I just fixed this completely.  It turns out that some
keyboards send a second ack byte after the reset, and this was not being
removed from the buffer.  Thus, the buffer was never empty, the
interrupt line didn't go low, and further keyboard actions would not
generate a new interrupt.  (Don't you love edge-triggered interrupts?)

Thanks to Holger Veit for cluing me in that there seemed to be something
wedged in his keyboard buffer after the reset.


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