Proposed resolution:

Change [valarray.cons], paragraph 2:

explicit  valarray(size_t);

The array created by this constructor has a length equal to the value of the argument. The elements of the array are constructed using the default constructor for the instantiating type T value-initialized ([dcl.init]).

Change [valarray.members], paragraph 9:

[Example: If the argument has the value -2, the first two elements of the result will be constructed using the default constructor value-initialized ([dcl.init]); the third element of the result will be assigned the value of the first element of the argument; etc. -- end example]