When you open some challenge and join it, there is the pop-up: "Challenge Accepted!".
You can close that pop-up by the button "Let's Do It" (it it's only for closing), but if you leave it opened - and return to challenges' page and open some other not-yet-accepted challenge - the pop-up will be there stating you already accepted that other challenge.
So the pop-up is global and just remembers if it's opened or closed, but it takes title, description and distance from current page, without checking if a challenge is accepted or not.
Pop-up after accepting a challenge:
Not-yet-accepted challenge with incorrect pop-up:
