Share map... Turns on layer unexpectedly.

If I share a map and open the map from the resulting link, I find a layer that's turned on inexplicably.

 

Does anyone know what might be the culprit? Even if NOTHING else is checked on and I choose to share the map, this particular layer is turned on when I open the map from the shared link. 

 

I don't see anything in my Site.XML that might be indicating this. The layer is default not visible for the theme that is linked from.