Here is a video I made of this bug.
https://youtu.be/Aj7v2mvectwThe skeleton was modified in editor mode in this level (matter not which level I make him in, or any character). When I open the level and save as and re-import him he looks exactly as he did prior to editing him. If, however, I alter the character prior to save as, he will appear as he should +the editing I do to him in GM mode.
This is an aggravating workaround, but it does not work at all for creatures that have no editable appearance in GM mode - such as a spider which I tried to make smaller. There is no way to get the edited creature to appear correctly in GM mode.