Working in 3DS MAX While keeping Unity open. Problem with objects going Invisable

Hi everyone im working on a apartment scene in 3ds max while letting it update in unity im finding though that when I cut holes in the walls and changes stuff in the max file parts of the unity scene goes invisble. Say if I cut a hole in a box for a tunnel then there will be two holes in the box when i refresh and update the unity scene.

Anyone know what the problem is ???

Regards