I'm a bit hasty with my friend invitations, and I'll often invite them before they've loaded into the game. They never see the accept / decline dialog because the game hasn't yet loaded for them, and they're stuck being invited. Currently, they have to log out and back in to decline the invite.

I think the easy solution to this is to automatically decline an invitation after it's been open for one minute without a response.

Confirmed this is still happening just within the last few days. Only way to clear it, like you say, is to re-log.