According to 9.6 [dcl.struct.bind] paragraph 3,

Given the type T_i designated by std::tuple_element<i, E>::type, each v_i is a variable of type “reference to T_i” initialized with the initializer, where the reference is an lvalue reference if the initializer is an lvalue and an rvalue reference otherwise; the referenced type is T_i.

If T_i is already a reference type, should this do reference collapsing? Presumably yes, but reference collapsing is specified in terms of a typedef-name or decltype-specifier, which are not used in this description.

See also issue 2313.