A) Frame-building:
After cut a bush which is blocking the building option of the watchtower the next problem will come after server restart.
The the bush comes back and block the building options for the frame which is now on the same position like the bush. Cutting down again will helps.
B) Roof-building:
After setting the watchtower and next to him a fence without building up first the watchtower (putting down trees, add planks and nails and build roof) in future moments the down trees of the fence will block the roof-build-option of the watchtower. Animation will start but at the end no building-results are there.