Hi Friedrich,
I guess it is somehow related. I can indeed see the .sav file when I select "all files". But to my surprise I can see .zsav file when only syntax and data is selected.
As far as I understand I have to define the mime type in the MSWindows registry. However I have done this for .sav and NOT for .zsav. To make things more complicated even if I remove the .sav mime type definition from the registry this doesn't make any difference.
The bug
https://bugzilla.gnome.org/show_bug.cgi?id=788936 seems to be in version 2.54 However I use glib2 2.52. Maybe it was in earlier versions too, but in the mingw libraries of openSUSE 2.52 is the latest version. So upgrading now would be a major task.
My first gues is that mime types are not handled properly anymore in my current toolset.
BTW it seems .ods importing is also not working correctly. I haven't looked at this yet.
Have fun