That's got to be a bug, but the only teleporters that I use regularly are the ones in the Misty Islands. I've always assumed that crossing a border with any teleporter costs nothing in food.
But I wouldn't notice necessarily notice that anyway. I only ever use those teleports once in a game, and that is merely for completeness. My default party (ACSS) has three characters capable of learning the Lloyd's Beacon spell, so once I've visited a place and set the Beacon I can always go back to it. I keep an eye on the time left, and renew them when they expire.