random viewport clipping

[Mitchell.AveryFB7CQ]

A colleague and I have both run into this problem in completely unrelated projects/scenes.  

The behavior seems to be that any geometry below the z axis is clipped specifically in the top orthographic viewport.  Even parts of a single mesh that sit below z=0 are not visible, but everything above the z axis is.  I noticed that if I zoom out far enough all geometry reappears.

This occurred with viewport clipping turned off, but enabling it and adjusting clipping planes had no effect.  I am having trouble reproducing this, it seems pretty random.  For both my colleague and myself, the problem was resolved by merging geometry into a new scene.

[MartinBeh]

What version of 3ds Max is this?

And can you try to create a test scene that shows this, e.g. by saving the scene to a new file right when it happens without moving the camera/viewport?