There are two discs for SKs which help when tanking by casting a big rune (the Mantle and Carapace lines, I currently have Tylix's Carapace and Krellnakor's Mantle). I see they're on different timers, so one should be usable while the other's on cooldown. However, in practice, I've only been able to get Krellnakor's to go off one time after using Tylix's. The other times, no message, nothing. I click the button for Krellnakor's and nothing happens. Any ideas what I'm doing wrong? Thanks!