as your progressing through the campaign and acquire more and more units in the armory, if u click on a particular unit it zooms in and can u see adjacent units the background IF u have them now if u do this with the siege tank and have the medivac, the medivac will disappear and will not be in the background as it is suppose too same with the banshee, the viking just won't be there (if u have the viking) but the firebat and marauder will show the adjacent units in the background
Sorry for being off-topic but your computer is a beast, you should get an SSD to make it go super saiyen