Windows 8.1 64bit
Nvidia GTX 970

Broken: 2.75a c27589e

If I change the units to Metric after adding a cylinder, then edit the Add Cylinder properties on the left hand side, (Number of vertices, Radius, or Depth) the Units change back to None. However, if I change the unites to metric before adding the object, then edit the properties, the units remain Metric.

Open a new blend in blender. Add a cylinder, then change the Units to Metric. Now try to edit the radius as 2.5cm. Then try to edit the depth as 10cm. You will see an error: unexpected EOF while parsing, string 1,4, 10cm. And you will also notice the units have changed to none.
Now delete the cylinder and change the units back to metric. Add a new cylinder and you should be able to edit both fields without getting the error, and keeping Metric.