Anchoring cast bar to personal resource display

[nKweo]

I've anchored the default casting bar to the default personal resource display (so they don't overlap anymore) with some very basic code:

CastingBarFrame:ClearAllPoints()
CastingBarFrame:SetPoint("TOP",NamePlatePlayerResourceFrame,"BOTTOM",0,-28)
CastingBarFrame.SetPoint = function() end --without this line the cast bar glitches/stretches

It works pretty well, but when the personal resource display fades (i.e. without a target) the cast bar has a tendency to anchor to random nameplates. So for example when I mount up or hearthstone, I often see a cast bar in very weird places. Any ideas how I can solve this glitch?

I took a peak at the WeakAuras code (as it allows anchoring to the PRD without glitches), but it's a bit out of my league to fully grasp what is going on there. Any suggestions are much appreciated!