I pushed a code change to the site and, for some reason I haven't been able to determine yet, the site is failing to initialize properly when launched directly from the homescreen on iOS. If you load it in Safari it's fine.
I'll fix ASAP.
Fixed. I just needed to ensure that older versions of the scripts weren't used.
I also noticed and fixed an issue with "Add to Home Screen" - if you have moved the map from the default location before you pick "Add to..." it would embed the new location and options in the saved URL, and every time you open the map in "standalone" mode it will return to those coordinates; this annoying if you were at a random location/scale and particularly annoying if you had "Save Location" checked. Now the saved URL parameters are ignored if running "standalone".