The culprit can be found in TBDMMAP file an is called - surprise, surprise - <Units>:
<?xml version="1.0" encoding="utf-8"?>
<DisplayModelMap xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.3.0">
According to Product Support current AutoCAD units are being used for the setting when display model is saved for the first time.
Just don't know why most of my DM have "Meters" as setting an only one "Millimeters"....
Map 2013, SP2