I just don't see the need for the suggestion's change, to be honest. If the AI is acting up, which your anecdote alludes to (one case doesn't make a bug, but it is something), I'd rather not band-aid it with a UA change.
Well, the tiles counts as city-connections anyways, what difference does it make if roads on those tiles are also free?
I mean sure, maybe the strange roads all over the place issue could be solved, but it doesn't really change the fact that the AI can't handle the non-road tiles connecting cities very well.
Ancient example, if you have two Iroquois cities that are almost connected (forest all tiles between them except for 1), the AI can't figure out to place a road on that one open tile, but instead builds a full road between the cities. There probably isn't a reasonable way to fix that behavior, but if the roads on the forest-tiles didn't actually cost maintenance the AI wouldn't suffer that much from it.
I mean essentially all this does is slightly buffing automation for those two civs (and neither of them have extremely amazing UAs), as well as helping the AI out a bit. I see no real good reason not to add it, unless it is a ton of work for you I guess.
EDIT: Also I'm not sure if I was unclear or something like that, but I did not mean this as a change, I meant this as an addition.