Cannot mastering horde maps because of this?! plz fix

My friends and I ran around 3 hours to complete the horde map on master difficulty.
When in wave 17, I got disconnected. My friend immediately pause the game, and I joined back in the game.
After 50 waves, the game just did not count my master completion.
This is bad.
Just because someone got disconnected for a min or two? Orz
TC could record every wave the players completed and it they’re all in master difficulity, the game should record the completion for the players.
Please fix this. This just ruined many players’ game experience, especially for those hard-core ones running master difficulty.