Ok i found this out when i was doing nothing and logged otu and back in.. So i tried it again, and again, and again and it worked. I'm pretty sure its a little glitch
STEPS:
1.)Log in, make sure you are doing the curst heart quest (Start it by going to a drug store person in any city)
2.)I think it may work on any monster that drops curst hearts (Try to go to ones that you find drop them more regularly)
3.)Kill a few of those monsters. You should .. SHOULD get a curst heart.
4.)Press esc, and click restart, to take you back to the start of the game.
5.)Log in again and choose the same character.
6.)Kill the same monsters again a few times, and you SHOULD get a curst heart again.
7.)Repeat steps 4-6 again and again for however many curst hearts you want.
I hope this works for you, becasue i did it about 10 times and i only had to kill about 5 bandits each time. Its notthe best way of training, but if you keep on doing it, youll get them at a much faster rate than normal. So you can delvl skills faster!