Steps how to reproduce with viking 1.6.2 (I use German UI Language):
So Each Save → Close → Reopen will add a new useless "Default Map".
I think the problem appears when opening the document. Source of "Standardkarten.vik" contains 1 reference "Standard-Karte" as expected, after having opened the file with viking a second "Standard-Karte" appears.
The behavior seems to depend on setting 'Edit → Preferences - Start - Add Default Layer Map' (Translated from German). Unchecking this one stops adding a Default Layer Mapp with every Launch, and currently I do not see any disadventage. So may be "Unchecked" should be the default setting?
Thanks for the extra information. Yes it depends on the auto added map.
I forgot about the case of opening a .vik file via the GUI.
It doesn't add the map when you load files via the command line.
I have fixed it in my code (yet to upload it), as now it deletes the auto added map.
The default will remain on, for simplicity for new users.
'More advanced' users can turn it off.