discard in fragment shader not working

Hey guys,

I use billboards for drawing spheres like in this tutorial
but with the driver updated from 304.60 to 310.32 the spheres won’t be displayed correctly anymore. The discard in the fragment shader is totally ignored.

Source code for the tutorial can be found here: https://bitbucket.org/alfonse/gltut/downloads

Driver: 310.32
Graphics cards: GTX 560 Ti and 680 Quattro (separate PCs)
nvidia-bug-report.log (495 KB)

Just tested 310.40, 313.26 and with a Quadro 2000M. Unfortunately, the bug is not fixed.

Just tested 319.17. Still not working.
Using another shader program with the same fragment shader but without the geometry shader, the spheres are displayed correctly (see attachment). So the bug has something to do with the geometry shader and the discard in the fragment shader.