*** I thought I had checked all the stairs but apparently some of them were two high. ***
The behavior I observed seems like a bug. I started a Rayas Children village in the desert next to one of the desert buttes. I get the Township quest and envision a sprawling temple on top of the butte dedicated to the Monkey!
You can see the tunnel entrance near the base, flanked by some wall lanterns. The “exit” is at the top, also flanked by lanterns.
I built the tunnel by using ladders and to get to the top and then tunneling into the edge.
The tunnel was created with no problem, as far as I can tell all steps are only 1 block in height but the Hearthings refuse to use these steps to perform tasks on the top of the butte. 
Is this set up too complex for the path finding or do they just not like to climb that many stairs? Has anyone else tried this with success?
EDIT - Release 687, no mods installed.