While lvling my dk (currently 85) I've noticed some fairly odd behavior from my death runes, after asking a few dk's in my guild none of them had the same experience.
Every once in a while (i think all the times out of combat) my death runes would convert to the unholy/frost runes. Now i'm not sure about the exact timing (how long after i got out of combat), but i know it hasn't been consistent. Sometimes i'm able to run around, die, get resurrected at GY (BG's) and still have 4 death runes up. While others i've had my death runes "reset" as i was switching targets in the middle of AV (granted i think that i did get out of combat for a couple of seconds)
At the same time i've been experiencing this in pve when sometimes they would reset between thrash pack pulls (at most 30 seconds apart).
Is a know glitch, and if so is there anything specific causing it ? (None of the runes were converted through rune tap / other rune generating talents)