I have seen this issue with bukkit before, but this is completely vanilla. Other players can break blocks and open doors but one user can no longer do this. The user can kill other players but that is it. This has just started happening today.
User is not an admin but can confirm other 'normal' users can play as normal.
Running vanilla 1.7.2 on Ubuntu. I have restarted the service and the user has rebooted their machine.
Is it possible that their user.dat file has some corruption?