I just ran a game using deadly gift and had a similar problem (Traps wouldn't display on the deadly gift interface despite having them in my inventory). Not sure if its a problem specific to the latest patch or just a recurring bug.
I fixed my game by saving and reloading. After that it would recognize all the traps I had in my inventory. I didn't have any further trouble with so long as I kept at least 1 of each I intended to use in my inventory.
Hope it works out for you.