We weren't home during your stay and apologize for any confusion -- that bathroom should have been yours and yours alone. We made clear to the other guests before we left that they were only to use the first floor bathroom. Obviously we were not around to enforce this, and for that I apologize.
Also, just to clarify, the third floor has a roof deck (no possible access from ground or other houses) that we leave open in the summer to create a nice cross breeze. We also apologize for any confusion regarding other guests. The rooms we rent are numbered and we mention other guests within the text. It has so far been clear to past guests but we will be sure to update our listings so as not to cause additional confusion!