Hmm works fine in IE and firefox for me, maybe its jsut opera. It does handle keystrokes slightly differently than IE and FFfor some reason... I haven't played around with opera enough to be able to make any suggestions, though.
For some reason, though, this is working my computer extra hard while the timer is running... cubetimer.com does this also. I dont know if its simply the routines used for displaying the times or what, but every time I start the timer my fan clicks on. Perhaps this is just a result of using development software such as mootools, but it would probably be a good idea to check on the efficiency of the code. After a quick glance, there is a ton of code behind the timer... way more than I'd expect for something as simple as stopwatch code. Although not a problem, perhaps a future goal should be working on efficiency