Alt+Tab + group invite = declined

When I'm alt-tabbed out of WoW, and someone invites me to a group, I hear the sound of the group invite popup, so I alt-tab back in to accept the invitation, but there's no invitation popup. My chat log shows that someone invited me to a group, but they tell me that I declined.

It appears that something in the process of alt-tabbing back into the game is causing it to decline a group invitation. Either that, or it auto-declined for me simply because WoW was minimized, even before I alt-tabbed back into the game. I can't tell.

Of course there's an obvious work-around to whisper them, explain that I was alt-tabbed, and ask to be reinvited, but I would prefer if the original group invite prompt remained on my screen so I could accept after alt-tabbing back into the game.

I am running Windows 7 64-bit, and this is WoW client 3.3.3, the current version as of the date of this post.