Accepted match and then the accept/decline option wouldn't disappear. Still there even after the match ended (which we somehow won despite me having the wrong runes, summs, and a champion I don't know how to play).
I don't know exactly what caused it.
I was streaming a vod of the LCS in the background when it popped up, noticing how laggy it was (because even on low spec with a good computer your client takes so much of my processing that I can't do anything else video/non-static-graphics related) I immedietly tabbed over to the video and paused it, planning to turn it back on once the game started (the game takes less resources than your client on low spec). I hit accept, noticed after a bit the countdown bar wasn't dropping and a notification popped up behind the accept/decline that someone had declined. Thought: "Oh, did I not hit accept after tabbing back in?" and clicked it again to since it was still up, and maybe that would still work. Nothing again. Then entered champion select and saw I was Ivern with Mundo runes, no flash, no snowball and spam clicked accept to try to get it to go away. Sound of the accept/decline display stopped after about 20 clicks, but didn't go away. Tried the same with decline, nothing. Went in game, had a good time, came out, couldn't honor, stuck in stats screen, can't X out. Am now going to end task.
P.S. Really salty that your client takes up so much resources if you didn't notice.