Are you using Compiz or Metacity? Metacity shouldn't stop you from dragging off the edge, but Compiz has a setting which disables it. If you're using Compiz, please go to the Move Window plugin and uncheck "Constrain Y". That should let you move it past the edge again.
Still, this is definitely a usability bug. Is it still happening, or has it been resolved in the meantime?
Are you using Compiz or Metacity? Metacity shouldn't stop you from dragging off the edge, but Compiz has a setting which disables it. If you're using Compiz, please go to the Move Window plugin and uncheck "Constrain Y". That should let you move it past the edge again.
Still, this is definitely a usability bug. Is it still happening, or has it been resolved in the meantime?