There are several different issues involved. As I started with recurves and went to longbows for years, and just these last few months back to recurves due to an arm injury, I will tell you what I think is the issue. The bow holding hand and wrist postion of each is quite different ( except for those longbows like the Columbia Blacktail that have a more recurve type grip. As taking the shot it supposed to be reflexive it is quite easy to put your hand in the wrong position when pushing that bow forward. The second issue with shooting bows of different draw weights is simply that they do not send an arrow on the same trajectory after the first ten to 15 yards. As so much of hitting the shot is both reflexive and confidence in your prior experience with how your bow performs, you are introducing a lot of variables and even taking away the automatic confidence you have in your bow's performance.