If a residential subdivision is along a lake, and the residents own land up to the shore, is it fine to draw the line for landuse=residential in the middle of the lake (where the property line is actually defined, though the residents don’t have rights to submerged land)? It renders fine, but are there any problems with doing this?
landuse doesn’t denote ownership, although in the case of small lakes I would not break up landuse=residential where the lake is.
The thing is it’s easier to extend it into the lake, since then one doesn’t have to match up every point with the lake to get the residential and lake colors adjacent. Are there any reasons not to go into the lake?
Your dilemma can be relatively easily solved by using multipolygon relations, where the coastline is shared as outer way between the 2 corresponding relations.
Other than that, this issue never got much attention since, as you say, it renders correctly in the major renderers.