[haste]

That requires quite a lot more work:

ReturnCastbar = function()
   -- Move the player castbar back to player.
   local castbar = YourPlayerFrame.Castbar
 
   castbar:ClearAllPoints()
   castbar:SetAllPoints(YourPlayerFrame.Health)
end
 
OnEnter = function(self)
   -- Move the player castbar to the raid frame we are hovering.
   local castbar = YourPlayerFrame.Castbar
 
   castbar.activeFrame = self
   castbar:ClearAllPoints()
   castbar:SetAllPoints(self.Health)
end
 
OnHide = function(self)
   if(castbar.activeFrame == self) then
      ReturnCastbar()
      castbar.activeFrame = nil
   end
end
 
-- on the raid frames:
-- Return the castbar if the unit disappears.
self:HookScript("OnHide", OnHide)
 
-- on the player frame:
-- Force it back when we stop casting.
castbar.PostCastFailed = ReturnCastbar
castbar.PostCastInterrupted = ReturnCastbar
castbar.PostCastStop = ReturnCastbar
castbar.PostChannelStop = ReturnCastbar

Might work.

Edit: No it won't, I'm completely missing the actual problem here being the initial anchoring, followed by re-anchoring when targeting a new unit. I'll throw some time at it tomorrow night or so.