Okay, I don't know why, but it's suddenly healing again on singleplayer. Not sure if it's a freak accident that it's working, or if they actually fixed it, or whatever, but I'll keep an eye on it to see if it stops working again.
EDIT: It stopped working again, but I'm not really sure why. It's like no matter which map, mode, or difficulty I play on singleplayer, the Hemoclobber starts out healing me, but then it just stops for apparently no reason after several matches. What I do know is that quitting and then restarting the game seems to fix it, at least temporarily. It still stops working eventually, and then you have to restart again.