Unfortunatly there is no progress. Also Wolfram has not sent any news (except of asking for the licence numbers). The behaviour actually looks like a bad bug, especially because it seems that the kernels are still used with >50% after finishing the evaluation.
Do you have access to Lightweight Grid Manager? Did you try configuring half the local kernels as "Remote Kernels"? I wander if the other half of the kernels could actually accept tasks if they are been managed via a different channel.