Combine - subtract work one way but not the other

[DrBwts]

SW2014, W10, x64

So I have a sphere & a square cross section extrude, they are not merged. I cut the sphere from the box & that works. Now I try it the pther way around & nothing the combine toolbox stays open & nothing happens. See pic below..

Any clue what's going on here?

 

[TheTick]

When subtracting the sphere from the box, there is a zero-thickness condition where the sphere face contacts tangent to the box bottom face. The parasolid kernel hates that.