I have noticed when attempting EV training on my mons, that if they are already at the badge XP cap, that they do not gain any EVs after winning a battle either nor do they gain any XP. I assume that not gaining XP is intentional, however I suspect that not getting EVs is not. Training EVs thus requires using a reverse candy so they can gain XP normally again.
Tested this on both game.exe and game-z.exe.