i've ran into the dreaded empty/blank pak map issue and as it seems links between obj. or lack thereof is one of the main reasons for this.
linking each obj. 1 by 1 in a map with a ton of obj would be nothing but a torture
fortunately it is possible to select an area by dragging with left mouse button! unfortunately if you are stupid enough (who? me?

however creating little pockets and then linking them seems to be a fine and easy way of doing things.