Just happened again to me with a 2nd drauger fang. Went to upgrade it on the Upgrade tab, realized I didn't have enough guck, left the menu and pivoted to the chest right there to grab some guck, went back to the forge and upgraded my drauger fang. Whoops, it's back on the creation menu!
This isn't fun at all, it's just a counter-intuitive and frustrating mini game. Sometimes it remains on the Upgrade menu, sometimes it doesn't. "Pay attention" isn't a solution. Please fix this. I love the game but this is seriously the dumbest part.