Panacea isn't the only one that isn't improved; Lesser Restoration, Restoration, Restoration Mass and Greater Restoration all do not get increased Caster Levels. Even though Raise Dead, Resurrection and True Resurrection all get boosts. And I am assuming Panacea isn't getting the increase, is possibly because the base spell was copied from a Lesser Restoration or Restoration spell base and then had the other parts added on (this is a common occurance, hence the Sun Bolt funniness I talked about in another thread as one of them was copied off the old FvS Silver Flame Capstone of Searing Light, hence it didn't have a Save).
So the Panacea spell itself might need to be reworked so it is counted as a normal Positive Energy spell.
J1NG