System Information
Windows 7 ultimate, Quadro 4000, Tesla M2050, graphics driver 332.50

Blender Version
Blender 2.69 r60995 - 64bit, also Portableapps version (same build)

Short description of error
increment snap does not work in perspective viewport with scene scale set to 0.01 and display > grid floor scale 0.01

Exact steps for others to reproduce the error
New scene, add cube mesh.
Set scene scale to 0.01
Set Grid floor scale to 0.01
Increment snap no longer works in perspective view, either as a main window or in quad view. Translation is smooth, with no jumps. Orthogonal views still snap as usual both in single and quad view.

Notes: setting the grid floor scale back to 1 allows snap in perspective view, and the snap is much smaller than the lines shown. However I loose the very fine grid for close up work. Currently switching back and forth on the grid floor scale between 1 and 0.01 which working on 28mm scale models.

Based on a (as simple as possible) attached .blend file with minimum amount of steps;