System Information
windows 7 pro and graphics card Quadro FX 880M

Blender Version
Broken: 2.72b hash9e963ae

Short description of error
Doesn't create proper sized proxies in the video editor when different sizes created at the same time

Exact steps for others to reproduce the error
load a png sequence 1920x1080 into the video editor and create all the jpg proxy sizes in a custom directory at the same time, they will have wrong very small sizes at 50%, 75%, 100% settings only 25% was correct

when I created the proxy only at 50% it made the proxy size correct