Why can't the compiler properly detect the type of Array!string("something")?

[Adnan via Digitalmars-d-learn]

In the following code the compiler says the type is 
Array!()(string):

                        if (key in wordTable)
                                wordTable[key] ~= word;
                        else
                                wordTable[key] = Array!string(word);

source/app.d(29,36): Error: template 
std.container.array.Array!string.Array.__ctor cannot deduce functi
on from argument types !()(string), candidates are:
/snap/dmd/99/bin/../import/phobos/std/container/array.d(467,5):   
     __ctor(U)(U[] values...)
  with U = immutable(char)
  must satisfy the following constraint:
       isImplicitlyConvertible!(U, T)
/snap/dmd/99/bin/../import/phobos/std/container/array.d(501,5):   
     __ctor(Range)(Range r)
  with Range = string
  must satisfy the following constraint:
       isImplicitlyConvertible!(ElementType!Range, T)