System Information
Ubuntu 14.04 64-bit
nVidia GTX 970
nVidia Driver: 352.30
CUDA: 6.5.14

Blender Version
Broken: 2.75a

Short description of error
When simple children of a hair particle system display count is set to zero, and render mode is set to cycles rendered in the viewport, no hair particles are displayed, even though when set back to solid view particles are displayed, and when rendered with F12 particles are displayed. A non-zero children count displays viewport rendered particles, as would be expected. Blender Render works properly, this appears to be only a Cycles viewport render problem.