DK runes are not functioning they way the originally did in 5.4 and even the ptr and beta they were working fine.
The problem seems to be around death runes from what I can see happening. Ok let me explain what is happening from A blood Dk perspective because what is happening is slightly different per spec. As A blood dk without talents no matter what you do you cannot turn your 2 blood runes into death runes they are only able to change with talents
Originally in 5.4 if you used Blood Tap or Plague Leech to turn A rune into A death rune and this rune was one of the permanent color runes like the Blood rune is for the Blood DK, you could then turn all 6 of your active runes into death runes which without said talents would not be possible for the Class.
Now Normally in 5.4 you could then as A Blood DK use those 6 death runes to do 3x death strikes back to back and then you used the Death runes that were originally blood runes they would also refresh as death runes A 2nd time because they were used by an ability that when used turned the runes used into death runes.
Currently on pre patch when you set up this same 6 death rune 3x death strike when the blood runes refresh after being used to do A death strike they come back as Blood runes and not coming back as the death runes they should be coming back as, this is 100% not working how the runes worked for the entire run of MoP of the first run.
Changing specs and then going to Unholy and using the same talents to then turn all 6 of your runes you should be able spam icy touch, or blood boil 6x times and be able to do it another 6x times forever but when you try this on unholy currently in prepatch something even crazier happens.
Go to A dummy A unholy open with 2 festering strikes to turn your blood runes into death runes, wait for all runes to refresh and then use ice touch. When the death rune that was A blood rune gets used it turns the unholy rune instantly into A death rune with no refresh time.
Runes are very borked right now not sure how when they were fine on the ptr of prepatch