[Tim Cullingworth]

I've had this a few times and I think it's when I've used the chat.

Nowadays if I type a message I make sure I then use the mouse to select something on the menu afterwards e.g. pits setup or timing.

I think what is happening is the chat window is capturing all keyboard inputs. Are you using the Custom shader, as I think they added an enhanced chat feature which I think might be causing the issue?