Comment 11 for bug 237604

It may be related to differences in the keypress handling in kernel 2.6, though. Here's someone reporting a similar bug in 2003:

http://lkml.org/lkml/2003/9/14/148

A person named Andries Brouwer replies with the following:

"The answers differ for 2.4 and 2.6. For 2.4 each keypress is a keypress,
and key releases are rather unimportant as long as the key is not a
modifier key. For 2.6 we have synthetic repeat, so a second keypress from
the keyboard is ignored, the key repeats with kernel-defined frequency,
and the repeat is ended by the key release."

If that's the reason, this bug must have snuck under the radar for more than five years! Though it would also mean that it's actually a hardware problem rather than a software problem.