Debian AMD64, 8 GB RAM, Radeon HD
Broken: current master, first noticed in december!!
Short description of error
Using an armature with "preserve volume" on a mesh with vertex weights produces a different (jaggy) result than in 2.69.
Exact steps for others to reproduce the error
I attached a .blend file.
Compare frame 176 in 2.69 with current git master.
Also press Alt+A to play the animation and you should notice a somehow jaggy animation in current git version.