Unit selection behavior with custom building.

[Medraut]

I duplicated a Hive, (everything is the same except I changed the unit actor model to a xel'naga shrine). In game when you drag to select units it filters out buildings after releasing the button. But this custom building I made overrides all unit selection if I include it in the drag box, leaving me with just the custom building selected and no units. What exactly controls this behavior?