I just tested with a Discovery_Walking_Guides map and can tell you that you can be lucky with your view.
Above map has a solid white border, all legends - like a scan of a paper map. Which definitely is not created by Locus, but rather integral part of that map itself.
Can you test your case by displaying one of your maps exclusively, alone (i.e. no overlay mechanics of any kind) and check how it looks like at its border.
If there is such border like in your screenshot, then it would smell like my experience with DWG maps - only "nicer" ...
Above map has a solid white border, all legends - like a scan of a paper map. Which definitely is not created by Locus, but rather integral part of that map itself.
Can you test your case by displaying one of your maps exclusively, alone (i.e. no overlay mechanics of any kind) and check how it looks like at its border.
If there is such border like in your screenshot, then it would smell like my experience with DWG maps - only "nicer" ...