I set tab as an extra modifier key. One of my hotkey combinations is tab+q. It doesn't work while running forward (holding w). It does work while running backwards or sideways (s, a, d), or while running forwards with the up arrow key. Tab+e works while running forwards. Tab+r works. Alt+q works. Just not tab+q, and only while running forward with the w key. When I changed the modifier key to caps lock, it still didn't work. When I changed it to the apps key (under right shift), it did. I have no idea why. I'll submit a bug report, but wanted to post in case someone has an idea.