At level 47, I got a level 47 epic quality axe -- Wolfsbane Hatchet.

I bought a Blazing Precise Runeshard (level 48 equip only) - and put it on the axe.

So a lower level item has a rune on it that supposedly won't go. I hit the same thing with a level 30 epic chest slot item - I put a higher level gear rune on it.

Uncommon and Rare items seem to honor the level limit but epics seem to have special rules about them so I figured I'd see if anyone knows about a limit to it or the like.

I'm not rich enough to go playing with how far this goes so I figured I'd check. Besides, the people in chat insisted it wasn't possible and said it was probably a bug but I don't think so -- just something different about epic quality gear.