It even bugs this way with "no walls" on:
Note that I thought the "no walls" text would appear in the bottom left corner, but at least link walking on water should erase any doubt I had it on. I'm thinking what caused this is that ZC thinks that maps have 8x8 as their max dimensions and anything beyond that is invalid and can't be traveled to. But zquest can acknowledge them, so you see them in the editor, but can't get to them in game.