Static Mesh Navigation Collision Properties Not Being Saved Correctly

Setting properties for a static meshes Navigation Collision and then reopening the mesh causes them to be reset.

This does not appear to occur in 4.14.3. This is a regression.

1. Open the editor
2. Add a Nav Mesh Bounds Volume
3. Add a Cube
4. Open the cube in the Static Mesh Editor
5. Under the Navigation section in the Details panel, add a Box Collision
6. Set the Offset and Extent to some number (I used 50,50,50 and 200,200,200, respectively)
7. Set the Area Class to NavArea_Obstacle
8. Save, then close and reopen the Static Mesh Editor for the Cube mesh

Result: The properties you set for the Box Collision are reset (sometimes some of them, sometimes all of them)

Expected: The properties would remain set to the correct values