Comment 28 for bug 274155

i get this as well, however i noticed that pressing any key - i choose a non-action key, shift - it'll continue to progress incrementally with the keystrokes up to a certain point where it continues on its own. it's something like 20 keystrokes before this happens.
this is during the loading bar that goes left-right-left-right back and forth a few times, then when it goes to the left-right that doesn't go back and forth it stops again, and a few keystrokes gets it moving again.

man i hope that makes sense.