I'm going to be a jerk and necro this thread because the bug still is not fixed as of 5.2. My apologies if you fixed it in 5.3 although I didn't see anything in the patch notes. (And yes I'm aware that you've been busy with urgent issues like crashes, so I'll cut you some slack.)
From Steam discussion ("Slaughtertorium?") started by me, Rhonin the Wizard notes:
There's a problem in the files.
Arena - says <UpgradesFrom>XenoAmusement</UpgradesFrom>, should be <UpgradesFrom>FightingPit</UpgradesFrom>
Slaughtertorium - says <UpgradesFrom>TournamentTech</UpgradesFrom>, should be <UpgradesFrom>Arena</UpgradesFrom>
HuntingGrounds - says <UpgradesFrom>SaughtertoriumTech</UpgradesFrom>, should be <UpgradesFrom>Slaughtertorium</UpgradesFrom>
