When I do paste special (command-alt-v), the glyphs I pasted move to the bottom of the fontview. And I cannot move them up again. This happens only when ‘All data’ is checked.
That helped me to get the glyphs back in the right place.
I noticed another behavior. When checking the position of the components I copied from the Roman file, I noticed that the components in the Italic file did not have the same horizontal position (x=0, y=0). Some had a negative position, others a positive one.
Does normal paste work, when I want to paste from one file to another (in this case roman->italic) with three masters ? I wanted to have the same components, metrics, position etc.