Shift operator, unexpected result

[JG via Digitalmars-d-learn]

I found the following behaviour, as part of a more complicated 
algorithm, unexpected. The program:

    import std;
    void main()
    {
        int n = 64;
        writeln(123uL>>n);
    }
produces:

123

I would expect 0.

What is the rationale for this behaviour or is it a bug?