Windows 10 16GB, GTX 965 2GB
Broken: 2.78.5(2acd05b) is broken along with every newer version that I tested.
Worked: 2.78.4(67bef6b) works as expected
Short description of error
There are strange dark artifacts showing up for simple blocks that are placed near one another. The artifacts that show up look like they are being baked in from some hidden object but there are no other objects hidden in the scene nor are there objects on any other layer.
The error happens for both CPU and GPU and also for 'Combined' and 'Ambient Occlusion' bakes.
Exact steps for others to reproduce the error
Open the included blend file and press bake.