It's strange how I found this post right after coming back in from my garage and had just experienced this very thing first hand.
I just finished my Osage longbow last week and that's all I've been pounding the target with since. I've finally started getting some good grouping with it and it's very comfortable to shoot.
Then I decided to take my Bear Grizzly recurve out and fling a few with it and everything was still grouping ok, but high and right?
So I put the Bear down and grabbed the longbow again and everything is back in the center of the target. I used the same method of shooting on both bows, and two different impact points.
Rather than get frustrated I put the Bear away because I plan to hunt with my own hand made Osage longbow and I didn't want to impede my progress that I've made with it.
Of course the recurve has a different grip and a completely different feel to it. I normally shoot it just fine, but evidently since I have only been practicing with the longbow I'm not one of those guys that can just drop one, pick up another completely different bow and put them in the center ring.