Linux Xubuntu 13.10, x64, kernel 3.11.0-15-generic
AMD Radeon HD6850 1Gb
Broken: 2.69.10 cc7cfd6
Worked: 2.69.0 r60991
Short description of error
Bevel modifier gives incorrect results (twisted and distorted faces) when applied on a mesh which contains vertices with five (or more) edges connected to it at certain angles.
Exact steps for others to reproduce the error
You can see attached blend file or make your own example:
Add a cube.
Enter to edit mode.
Extrude individually front and side faces according to their normals, so you get a L-shaped mesh block.
Select all three top faces and move them to the front by about 1 unit.
Add bevel modifier to see a bug in the inner corner of a block.