Nieuport 11 skinners, do you have this problem?

[The_Shadow]

Hello, I was going to try to make some historical N11 skins, but found out that the wire frame layer and the color layer tend to shift out of alignment (up and down), when I know I haven't done anything to cause it.  And I can close the file without saving, and when I re-open it, the layers are still shifted out of alignment.  I am working with GIMP.  Has this happened to anyone else, and what can I do to stop it?  I'm sorry I don't have any screenshots to show.