Construction:InternalSource is primarily used for radiant slabs. I don't think it would really apply here.
However, I have just now tested the SurfaceControl:MovableInsulation and I wasn't able to get it to show a difference in the construction U-factor or the interior surface temperature either way.
Sorry if that isn't of much help for you at the moment but it is good to let the EnergyPlus developers know when there are problems with the simulation engine.
I suggest submitting a ticket to the Energyplus helpdesk found here: