I tried to look for another post that was about this, and I couldn't find one. I am very sorry if someone has already pointed this out, but since it's been doing this since Cataclysm, I figured I might as well post about it.
For the tooltip on all items (or almost all?), regardless of whether it is a Heroic item or dropped from a boss on Heroic, it says:
Boss: [insert boss name here] (Heroic)
I use the latest version of the app on my iPhone 4.