Merging layers problem

I am trying to merge two frame to frame animated character layers, one layer contains the head and the other the body. I have completed both layers and now trying to merge them to be easier for me to colour them, however, when I attempted the merge, one layer flipped vertically for some reason. I usually animate and draw on the camera view. So I went to check the the drawing view and the body layer was actually flipped in the drawing layer for some reason I don’t get, while it looks perfectly aligned in the camera view.

Any explanation as to why this has happened? and how come the layer is flipped in the drawing view while normal in camera? any suggestions how to fix this?

Many thanks!