There is a loophole in the Bedroom Tax which means 40,000 of the people paying the tax may be exempt. This is because they made an error drafting the law.
The error affects working age tenants in social housing who have occupied the same home continuously since 1996. An oversight by the Department for Work and Pensions (DWP) when writing the law means that the housing benefit regulations dating from 1996 were not updated when the coalition legislated for the bedroom tax.
Since there are no rules about paying back money from the DHP, this means that when people are refunded they may have actually made a profit from the bedroom tax!