I discovered this in 2.76, I upgraded to the official 2.78c release and it's still there. Happens on both of my computers. This is a simple settings related bug.
The deforming checkbox in rigid collisions should be visible for "Final" as well as "Deform".
In depth description
In the rigid body collisions panel, there's a selection menu for "source". The options are in the following order:
at this point, set the shape dropdown to "Mesh" <
If you set the source to "Deform", a checkbox appears called "deforming". However this checkbox disappears for "Final", even though changing it's state inside "Deform" has an impact.
Steps to reproduce
0. 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. Leave it unchecked.
- Add two shape keys to the cube
- In "key 1", pull two adjacent top vertices of the cube down to make it into a slope.
- Keyframe the shape key so at frame 20 it's at 0, and at frame 30 it's at 1 (so it goes from being flat to sloped).
- Add a second cube, and make it a rigid body too.
- Place that cube above the first one.
- If you run the simulation now, it will ignore the cube below changing shape. As expected.
- Go back into the first cube, and check that "deforming" box.
- Running the simulation again, the cube will slide off when the shape key changes.
- Disable "deforming" again, and change the source to "Final"
- Note that the checkbox disappears
- Running the simulation now, the cube will not fall.
- Change the source to "deform", check the "deforming" box and swap the source back to "final"
- Running the simulation will show the cube now falls.
That checkbox should not disappear between final and deform, as it has an impact on the situation.