Solid Disappear after any Operation (e.g. union two solid)

I have some solids.

The solid will disappear when any operation is performed on them. 
e.g. Union solid A with B.

Kindly help if you have any clue 

Original 

After Union, A and B disappear 

However, the element is not lost but somehow select-able. but its not visible in any view (wireframe, transparent, illustration,  etc.)