I ran Naxx10 the other night with my GM, and when we killed the first boss of Spider wing (first wing we went to) I decided to burn Heroism, because why not.
So we killed him, then when we got to Widow, I completely didn't notice the fact that I was able to pop Heroism again, despite it being nowhere near at least 5 minutes between the 2 bosses. So, I finally noticed when we were up to Maexxna, and I watched after we killed her that the debuff disappeared. And this happened after we killed every boss.
So, did I miss something in a blue post, or is this a bug?