Reappearing error with sorting

[nnk]

It is quite strange, but the following code sometimes produces a
"core.exception.asserter...@c:\d\dmd2\src\phobos\std\array.d(253): Attempting
to fetch the front of an empty array" while trying to sort the array and
sometimes runs just fine:

import std.stdio,
       std.random,
       std.math,
       std.algorithm;

struct Point {
    double x, y;
    static Point opCall( double x, double y ) {
        Point nPoint;
        nPoint.x = x;
        nPoint.y = y;
        return nPoint;
    }
    double angle() {
        return (atan2( y, x ) / PI * 180);
    }
}

void printAngles( Point[] contour ) {
    foreach( Point p; contour )
        writef( "%0.1f ", p.angle() );
    writeln();
}

int main()
{
    Point[] path;
    path.length = 5;
    foreach( inout p; path )
        p = Point( uniform( 0, 100 ), uniform( 0, 100 ) );

    printAngles( path );
    sort!("a.angle() < b.angle()")(path);
    printAngles( path );

    return 0;
}

Using "a.x < b.x" as a sorting criterium produces normal behavior, so I guess
the problem is caused by using a function there. I'm new to D, and so I have
no idea, where exactly the source of this problem lies. Can somebody point me
in the right direction, please?

I'm using the version 2.037 of the compiler with phobos.