System Information
Win7 64bit, GTX 560 viewport, GTX 970 render

Blender Version
Broken: 2.75 official

Short description of error
In the "N" side panel under Transform there is Dimensions x, y and z. You can't edit more than one of them at the same time. The Scale works as expected.

Exact steps for others to reproduce the error
Select an object
Click and drag over Dimension X, Y, Z
Enter a new value, Enter, nothing changes
Click and drag again, this time drag the mouse also to the side - only one of the Dimensions changes