I found it! The answer was yes, I was missing something. This is a gnome bound key combination to switch panels. I found the setting using:
gsettings list-recursively | grep -i Tab
and replaced it by using
gsettings set org.gnome.desktop.wm.keybindings switch-panels "['<Control><Alt><Super>Tab']"
Then, since Gnome wasn't overriding my ...