GIMP, like Photoshop, is a complex tool for people who know what they are doing, nobody in that category would be confused by such a situation especially if GIM

GIMP, like Photoshop, is a complex tool for people who know what they are doing, nobody in that category would be confused by such a situation especially if GIMP shows a warning dialog in case there would be data loss when saving (something that GIMP knows about). Photoshop has that workflow to entrench its PSD file format. GIMP seems to want to do the same thing instead of treating all formats as equal (technical differences - which can be warned against - aside).