Collectible Card Game Headquarters

Hello! This is my first post so please be kind. While playing modern using Fiendslayer Paladin, he was targeted and killed by Murderous Cut. Ultimate price and Sultai Charm (destroy target monocolored creature) worked too. The 'Fiendslayer paladin cannot be the target of red or black spells...' effect is not working properly.

Good luck with that bug, I hope you guys fix it soon.
Congratulations to the developers for the fantastic work they have done so far!

Which Engine are you using (Forge, XMage, Magarena, etc?)