Underwater tiles defined unreachable until dupe told to travel to closest reachable tile.

Using a mac. 

Tiles which duplicant must cross several (it seems to be if the path through liquid is 10+) liquid filled tiles to reach (encountered both vertical and horizontal) are classified as unreachable until manually told to travel to the nearest reachable tile and set speed to game speed to 1x. Once they get close, the formerly unreachable tile becomes reachable for traveling, but jobs do not necessarily become reachable.

This a particular nuisance when trying to dig/build in remote areas.

Duplicant moves fine horizontally through liquid only one tile high.