PU shouldn’t make voodoo hurt opponent, though. It copies it, it doesn’t make a new one and damage it. The damage was a bonus voodoo-specific function that had to be explicitly added to make voodoo usable. When you PU a damaged martyr, it doesn’t double its buff.
Based on that, in my opinion, the problem here is that voodoo needs the card text “damages opponent per missing hp when copied”