Proposed resolution:

Change [meta.unary.prop], p6:

the predicate condition for a template specialization is_constructible<T, Args> shall be satisfied, if and only if the following expression CE variable definition would be well-formed:

• if sizeof...(Args) == 0 1, the expression:

  static_cast<T>(create<Args>()...)
  T t;
  

• otherwise the expression:

  T t(create<Args>()...);
  

[ Post-Rapperswil: ]

Moved to NAD EditorialResolved, this issue is addressed by paper n3047

The specification of is_constructible<T,Args...> in N3000 uses

static_cast<T>(create<Args>()...)

for the one-argument case, but static_cast also permits unwanted conversions such as void* to T* and Base* to Derived*.