Windows 7 64 bits
CPU: Intel i3-4170 3.70GHz 2 Cores, 4 Logical Processors
GPU: NVIDIA GeForce GTX 970
God Mode Enabled
As seen on the save and the video, it seems easy to replicate if you use God building to get your garrison and the 5x5 empty area on the East side of the map. On normal circunstances with just clicking on the terrain and letting the workers do their job they eventually claim the land and reinforce the walls (also seen at the end of the video) and they also do their job properly if you drop them yourself as close as possible.
At first i though it might have something to do with God Mode, as it is usually the case, but i have God Built non-reinforced earth tiles in other areas of the dungeon and the Workers seem to work just fine with an inmediate response, and even with the involvement of God made rooms and land, that still doesnt explain why the Tavern has been ignored.
You can see how creating a few corpses for the workers to pick up made them go to the ignored area and then they forgot to come back to finish the rest of that area. You can see Workers moving from the lair to the 7x7 Garrisons only to do a 180° turn and go back, going from "Collecting Corpse" to "Collecting Item", possibly alluding to Micro Piglets for the Tavern since there is no blueprints or any artifact that needs to be picked up, but they also bug out and do a 180° again and go back to trying to "Collect Corpse". These repeat a bunch until another worker ends up doing it, and even so there are times some of them try to do the corpse collection when there is nothing left on that area and only notice when they are already there.
The fact they change behavior back and forth when they DO notice makes me think there is no communication between the workers as to who deals with what.
You can also get them to notice the walls by making a construct or a blueprint of a defense or just good old digging, and once they finish they go after the walls that are right there.
Cant say the same for the tavern. They still ignore it.
Customer support service by UserEcho