The amendment should have been dropped. More importantly than what it disallowed, it allows Congress to authorize indefinite detention - "unless an Act of Congress expressly authorizes such detention." A bill that authorizes Congress to do something unconstitutional is both unconstitutional and sets a very bad precedent. Congress quite clearly can not authorize such detention.

"An authorization to use military force, a declaration of war, or any similar authority shall not authorize the detention without charge or trial of a citizen or lawful permanent resident of the United States apprehended in the United States, unless an Act of Congress expressly authorizes such detention."