On Sunday I ran the Druid's Deep series with my level 17 artificer (on heroic normal), and while doing so I found "corruption of nature", when I found it the runearm said it was min level 15, so I equipped it and finished the rest of the quest with it equipped and used it the rest of the day.

Cut to this morning, I sign on my Artificer and noticed that he didn't have a runearm equipped. Checking my inventory I see that "Corruption of Nature" now has a minimum level of 20 on it. What gives?