For what it's worth, I had the same problem with one particular bow, and the reason turned out to be that I was overdrawing it and mashing my finger down onto the knock.
I now shoot 3 under, but that's because I like it better and shoot better that way. It also eliminates the problem you're having but I won't change my whole style just for that.
If you're getting porposing with both styles, I'd say Tilzbow is right on with his #1 suggestion. The best solution I can think of is to go bale shooting - get about 5' from a target that's big enough you can't miss, close your eyes and concentrate on pulling your draw elbow straight back away from the bow parallel to your bow arm and your arrow - otherwise known as Terry's form clock.