[GAMEPLAY] Tiamat Bug

I was recently playing a game as Shyvana and attempting to build Titanic Hydra. On two occasions when I tried to buy Tiamat, the space in my inventory previously held by Rejuvenation Bead would go blank, but not be filled by Tiamat. The gold was gone, but I didn't get the item. I'll have to try this a few more times to see if I can reproduce it again, but this is a pretty serious issue because it caused me to lose ~2,400 gold.