I am getting a 5 minute CD on rapid fire when I swap helms with the Rapid Killing runes. i.e. swapping from t1 helm to crown of destruction. I will always get a 5 minute CD. The CD also always refreshes if I swap helms before the 5 minute CD is up. Once the 5 minute CD is up from swapping helms, the CD of Rapid Fire is 1 minute. This defsus.
They did this to prevent rune swapping while things are on cooldown. They did this with a bunch of other things too. Like all Priest defensive runes share a cooldown.
I think it’s Shadowstrike puts Mutilate and Saber Slash etc. on a cooldown so you can’t Shadowstrike swap runes.