I got the normal version of Erethos, the Empty Promise and I upgraded it, although when I hit the threshold to heroic gear, I gained the heroic appearance, but I also lost the normal appearance 
Did you equip the item first prior to upgrading it? I imagine that might be necessary to lock in an appearance, but if you didn’t, additional info on the steps you took would help your report.
I thought I had, I already put in a support ticket in game and they told me to report it here, as it’s being an issue that’s happening to a few people. Cause when I got the staff it did say I aquired the apperance.
The same thing happened to me. To make it worse I got the LFR appearance today. I upgraded it to get the normal appearance back. I check I had the LFR, Normal, and Heroic appearance. I logged out and when I logged back in the LFR appearance was missing. This really needs to be fixed.