Council Tax - Universal Credit - system really unfair

I was pleased my son was awarded the amount of Universal Credit which Citizens Advice Help to Claim forecast, but today Council Tax wrote to me that my son now has to pay some Council Tax whereas before he got full Council Tax Support - this is despite the fact that he is getting the same amount of benefit with this migration lark as he had before. It would appear the reasoning behind the Council Tax is either the New Style ESA or the Supported Permitted Work which my son does, 3 to 5 hours per week which was disregarded for Council Tax before. The wording of Supported Permitted Work has changed on Universal Credit to "earnings" which sounds very grand. Maybe my son should stop doing the Supported Permitted Work which is what it is still called under New Style ESA, but it is therapeutic for him so not good to stop.