Hi there,
Right from the start: Please excuse my poor English, I am not a native speaker.
Yesterday I ran RFC on my WL and in the group was another WL. We noticed about halfway through, that we only ever had one Corruption on each target active. We tested it, and whenever one of us cast his Corruption the active one was overwritten.
I thought maybe it is just a visual bug that made the damage numbers disappear, but when I started with Corruption and then he cast his, the damage even disappeared from the combat log.
I know about curses (only one per WL), but if this is not a bug: I played loads of WL in TBC and WotLK and never really noticed this; is only one Corruption per target possible in Vanilla?
PS: On my Warrior I noticed something similar happening with the Rend debuff.