Windows 7 Ultimate x64
NVidia Geforce GTX 560 Ti Driver version 332.21

Broken: 2.69.8 5611fb6
Worked: 2.69 stable release

the Ctrl+B bevel fails when used on certain faces, or edge loops.
It always fails on a cube's face, and it varies unpredictably depending on topology. For example, It works on a cylinder's 'cap' but if used on a cube afterwords, it will always twist the beveled face of the cube.

The behaviour is not predictable, but can be repeated with the following steps consistently.

1. Start blender
2. Enter edit mode with default cube selected
3. Select any face
4. use Ctrl+B bevel (Percent/Depth/Width/Offset) - FAILS
5. Delete the cube and add a cylinder
6. Bevel the cap of the cylinder - WORKS
7. Add another cube somewhere
8. Bevel a face - FACE TWIST