That's the CD extended feature.
Toggle it on/off by pressing the 5 key. It doesn't show all unit ID'ed because it is based on Platoon formation. For example you choose a squad on a particular platoon, then all squads on that Platoon will be ID'ed. If you choose HQ A0, then his immediate subordinate (including Company commanders) will be highlighted.
The regular "Show unit ID" in preferences/game settings dialogue is used for debugging purposes, it's different from this feature.
Just curious why didn't you upgrade to the latest version 2016?
Oh, and welcome to the forum!
