That's a great question!
I've written up a solution article that hopefully explains things:
I agree its probably not as intuitive as it could be, and I'll forward this on to our Product team.
I'm trying to save the changes I've made to the layers on a map I'm working on. I started with an OpenStreetMap as my base map.
I've played around with hiding some of the roads, hiding the names of the suburbs/parks/rivers, hiding the visibility of some of the layers (like Points of Interest) as I want just a basic map with the major roads on it.
When I achieved the look I desired, I tried saving my map using the green save button at the top, as well ensuring that the bookmark function with the "Update bookmark extents using current map extents" box is ticked (and then clicking on the green save button again just to be safe), but every time I go back to my map, the road names and layers I've hidden reappear.