Bug or Feature: `this` necessary to call function with template this parameter

[Q. Schroll]

struct Example
{
     private void helper(int i, this X)() { }
     void funcTempl(T, this X)(T value)
     {
         this.helper!0();
     //  ^^^^^ Why do I need this?
     }
}

void main()
{
     auto ex = Example();
     ex.funcTempl(1);
}

The question is in the comment in the code. Is that intentional 
or a bug?