There have been many times when I’ve put up a correspondence challenge, did something else for a moment, and find that someone has accepted the challenge and immediately canceled the match before I had a chance to respond. This can be very frustrating since I have to re-post the challenge (sometimes multiple challenges).
I think what is happening is that the accepting party is expecting to play a few moves in live time. I don’t think this expectation is fair, since correspondence time assumes turn times of at least hours if not days.
What I would suggest is that if a correspondence game ends in cancellation, a duplicate challenge should be posted automatically. This way the accepting player is still free to cancel, but the challenging player isn’t snubbed.
There would have to be some adjustment to make sure a challenge isn’t automatically posted when the challenger doesn’t want it (perhaps a timed confirmation pop-up?), but I think it would be easy to come up with a solution.