I have experienced the exact same issue, but for all my powerframes - I already posted it in "oUF - Layout discussion":
http://www.wowinterface.com/forums/s...=18363&page=50
I suppose referencing the powerbar to the frame itself insted of the healthbar might do the trick for me too - will check later today. Thanks.
However, why isn't it possible to parent the healthbar-frame to the powerbar one?