Can anyone illuminate me as to where this destructor call is coming from?

struct Thing
{
  static int x;
  this(typeof(null)) pure {} // <-- comment this line and the error goes away
  ~this() { ++x; }
}

Thing fun() pure
{
   return Thing(null);
}

error : `pure` function `urt.string.string.fun` cannot call impure destructor `urt.string.string.Thing.~this`

Shouldn't NVRO construct the result in place and elide the copy/move? I would not expect any call to the destructor in fun()...

Also surprisingly, if I comment out the constructor, the compile error about the destructor goes away. I can't see why the constructor's existence affects the destruction semantics in fun()?