Here's a picture of the effect. Regrowth, triple lifebloom and trying to cast rejuv on the MT. Assuming the fight wasn't over right there, after landing a rejuv I'd have a couple of seconds to raid heal some random targets but instead I get a non-cast and if I don't notice it then Rejuvenation drops of the MT. Either way it's a wasted effort.
If I am correct in the behavior of this talent then for it to work in a more useful way it should trigger a separate replenish buff on the target and not be interwoven with the exclusive procced rejuv. If the rejuv would be removed by a Swiftmend then I suppose the buff should be removed as well. If a new rejuv without a replenish proc were to be applied to the target then it should not reset or affect the replenish buff, just reset the rejuv timer.
If Replenish isn't the culprit then there's some Holy/Disc priest spell that conflicts with Rejuvenation or it's some random short-term spi/sp buff that procs from another class which would increase my healing though that wouldn't explain why only Rejuvenation suffers.
Update: I found a forum discussion about this subject as well as a bug report.
I quote Allyine of Azgalor in that thread saying
The bug occurs when a few different things are up:
- You have the Replenish talent and are trying to recast Rejuv while one that proc'd Replenish is on the target
- You cast a Rejuv with some sort of spell power proc up, such as a trinket, that creates a more powerful Rejuv on the target and the buff has since fallen off so you are trying to refresh a stronger spell with a weaker spell
- You cast a Rejuv in tree form, shift out and try to cast another less Rejuv in caster form
Thus to summarize it would seem that the loss of an spirit/spell power buff or a procced Replenish would cause this error. In my case it's very likely Replenish because I'm not using trinkets with spell power buffs and this happened to me last night in 10 man Naxx in a group with no shaman and everyone was alive, standing still on Patchwerk with all regular buffs up.
I'm going to respec without Replenish and test this on the next raid reset to confirm if the error goes away.
Another update:Thank you Keeva for pointing out the following:
Allyine (the OP of the thread) goes on to say:
"It's not replenish. I spec'd out of that and the problem still happens to me. "
The mystery remains...
Another update: I just browsed our WWS from last night and looked specifically at our Patchwerk fight. I found another likely candidate: [Demonic Pact]. The tooltip states "increases spell power by 10% of your Spell Damage for 12 sec". I'm not sure how to interpret this. There's Bonus Damage and Bonus Healing and then there's Spell power. Does Demonic Pact take 10% of my Bonus Damage and apply it to Spell power thus raising my Bonus Healing?
Watching the numbers in WWS I could see my Rejuvenation ticking for amounts such as 1989, 1990, 2109, 2110, 2144, 2159, 2203. Assuming that I had somewhere around 2140 bonus healing that would explain the 10% increase from say 1989 to 2203 during the fight due to the Demonic Pact buff. If the warlock used spell power trinkets at the time when Demonic pact procs that would also explain the fluctuation of the numbers as 10% of his spell power would vary.