Hi Udo,
the problem with your image is easy to solve. You only have to change one of the options in the FITS module: Open "Format explorer", select FITS and click in the button "Edit preferences" to open the options of the FITS format. Change the option "Coordinate origin" to "Lower left corner (bottom-up)".
Now when you save a solved image, the result will be compatible with applications that expect this coordinate origin.
Juan designed the XIFS format because of many problems like this with the FITS format. The funny thing is that this is unambiguously defined in the FITS specification (the files should be stored bottom-up). However historically the amateur tools have saved/read FITS files "Up-bottom". Old versions of PixInsight defaulted to the "professional" standard but I suppose Juan changed it to "Up-botton" to maximize the compatibility with other tools, although this not seems to be typical of Juan
.
Andrés.