Simply put I can't imagine I'm the first to post this as its pretty evident. When the Operator assembles the Darter, it creates a duplicate "ghost" UAV Bag. The bag is selectable but after selecting Take UAV Bag, the bag disappears but nothing is placed into the inventory (which is good since the Darter is still there)

Disassembling the Darter creates a "real" UAV bag which is placed into the players inventory. This is still true as of this posting with the latest dev branch update in place.