Why does JKR's Direct Focus work sometimes and not work sometimes against DR squads

As stated, marked shareds the same priority with taunt. You should be able to equally select characters that are either marked or have taunt. Counter attacks will randomly choose which one to attack. The only reason this should not work is if you mark DR (no assists will occur but DR should still be marked), or JKR has Corrupted Battle meditation, so he can ignore taunt and call the assist but the enemy selected will not be marked because he can't inflict debuffs with CBM.