If I press volume down, on either the device or the phone (unified volume control) the volume goes down like normal.
If I press volume up, on either the device or the phone (unified volume control) the volume ALSO goes down. Watching the volume display on he phone as it happens reveals the volume slider stepping up one level, then slipping back down to a position slightly lower than it was initially. Repeated presses of volume up drive the volume down further to the point where sound becomes muted.
Since this is happening with three COMPLETELY different bluetooth devices (A desktop speaker, a headset, and a Home Theater System) and this is NOT happening when I connect using my Samsung Galaxy Tab Pro 10.1, I can only assume something on the Moto X is to blame.