They knew damn well the foster carers thing was wrong. Amendments made in the Lords would have taken foster carers out of the scope of the bedroom tax - the government insisted on putting them back in. They've only reversed it now because people have noticed what they are up to.
Disabled adults will still suffer, as it seems will victims of domestic violence. The bedroom tax is completely unfair, ruddy cheeky from a government that is still failing to build enough houses (and was the party who sold off council housing in the first place, although the Labour government failed to do enough here as well). Especially cruel at a time when they are giving the rich a tax cut.