I discovered this in 2.76, I upgraded to the official 2.78c release and it's still there.
Short description of error
For Rigid bodies of Shape Mesh there is a deform option that is only visible for Source of type Deform.
However, this option can affect other Source types.
Steps to reproduce
- Open blender
- Make the starting cube a rigid body
- Check the "animated" box (so it doesn't fall away).
- Set the shape to "Mesh" inside "Rigid body collisions"
note that a "deforming" checkbox has appeared just below.
That checkbox disappear with "Final" and "Deform", but still has an impact on the simulation.
Edit: Developer note: