sphere clipping problem

Thanks in advance.

I just wrote some codes to draw a large sphere,
placed a camera inside and near top of it.
It was just for using as a sky sphere and applying atmospheric scattering to that.
But the part of sphere is clipping under specific conditions (like keeping pushing print screen key)
or always as you can see below.
http://tempsend.com/E62DA4F7CF/ACDF/Abnormal.jpg

In some cases(I don’t know exactly when), it is correctly rendered as below.
http://tempsend.com/50D2B2CBAF/FDE7/Normal.jpg

For more informations, source codes and executable are included below.
http://tempsend.com/BADE119DEF/509F/SphereClipping.zip

Strangely, it never happens on ATI(AMD) graphics cards.
I don’t know why, anyone has an idea?