Most of the discussion of this bug can be found in the report of bug #124406. Since several bugs with similar symptions are being discussed in that thread, I thought I'd separate this issue from the discussion for which we know what is going on and for which there is a fix upstream.
Steps to reproduce:
1. Type a command into a console window in X that involves sudo and will generate some processor and/or disk activity, e.g. 'sudo apt-get upgrade'
2. Press the Enter key and hold it down for about half a second, so that there is CPU/disk activity when the key is released.
The X server will not receive the key up event until after a few seconds later, so autorepeat will kick in and generate lots of 'Enter' events.
A surefire way to trigger this bug is by doing something like 'for ((;;)); do sudo apt-get upgrade; done' and then trying to type something in a different window, you'll notice that key presses are delayed.
This turns out to be a scheduler issue where a task's vruntime wouldn't be reset when the task was moved between groups. The (essentially two-line) fix is included in the upstream 2.6.25 release. Here's the relevant git commit:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=810b38179e9e4d4f57b4b733767bb08f8291a965
I've copied the debdiff fixing the issue on the ubuntu kernel from the other thread. It's causing absolutely ZERO new issues on my system.
Absolutely confirmed, I regularly get a dozen or more blank lines after I hit enter to do a sudo apt-get operation (because the enter event is being repeated). It's extremely problematic because of being associated with sudo (e.g. I don't get to answer Y/n to apt-get, I get the default picked and if I'm lucky I can ctrl-c it before it actually happens, so I can review it).