Maybe some knows it already maybe most not yet.
You can try it on test-server-dummys, its live since summer, I didn't know it.
As it was:
If at time of trigger of the rune you where casting or you where stunned, the heal over time would not be triggered.
As it is now:
Casting or not, the hot will trigger on the runes fade.
Stunned or not, the hot will trigger on the runes fade.
But: receiving multiple stuns (like 6 stunning blows right at trigger time) will may make if fail.
My setup for testing:
approach 1:
6 test-dummies lvl 88. All attack on. Aggro all of them and get hammered, chaincast wahrd and any other spells you like and get stunned as much as they want. 100% trigger success at all my tests.
approach 2:
6 test-dummies lvl 88. All attack on. Befor start aggroing: Position yourself right in the middle of all and launch an PPAE. You will receive 6 swings at the very same moment consuming the rune and applying multiple stuns. Under this condition the hot may trigger but had something like 50/50 chance. This setup is a construct and doesn't reflect real situations.
My conclusions:
Spell is fixed and really nice now. There has been code added to bypass stuns and to let the hot start even if you are actively casting something.
Receiving multiple stuns at the very moment may lead to a situation where the "bypass part" is evaluated and right befor the hot is triggered a "new" stun blocks again. If you find yourself in a situation where multiple lvl 88 mobs are hammering on you, the ward won't save your life neverthless