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I've implemented a fix for this, but as the rest of the dev team have gone home, it won't be able to go live until QA and Easty are back on shift in the morning.
In the meantime, I'd either avoid the abandoned rune dragons on your world, or focus fire from as many players as possible to clear them out. They won't switch phases, so you won't have to deal with the flying phase.
The issue occurs if someone attacks a rune dragon until the 1/3rd lifepoints berserk phase, then leaves it out of combat so it regenerates back to full lifepoints.
Bear in mind this can happen with the regular and the elite dragons. Elites aren't aggressive, so you should be able to steer clear of them, while the regular dragons are aggressive but do less damage (hopefully tankable with the right setup).
If you see a rune dragon with more than 33% lifepoints with a glowing crest on its forehead, that's the indicator that it's enraged, and will stay enraged until killed. Approach with caution!
From a thread in RGU. Would be useful for avoiding the berserk phase of rune dragons
Lurk
15-Jun-2015 19:57:28