Type inference oddity with this_program

Example code:

constant label_xyz="XYZ";
int main()
{
    foreach (indices(this_program),string const)
    {
        //program me=this_program; write("%O\n",me[const]);
        write("%O\n",this_program[const]);
    }
}

This produces the following error:

thisprog.pike:8:Indexing on illegal type.
thisprog.pike:8:Got     : function( : object(is
program(/home/rosuav/thisprog.pike))).
thisprog.pike:8:Index   : string.
Pike: Failed to compile script.

If the program is retained in a separate variable (see the
commented-out alternative), it works fine, and correctly fetches up
the value of the constant. Using this[const] also works fine. But
this_program[const], for some reason, is thought to be looking at a
function (which it kinda is; calling a program will return an object
of that type, so the signature is more-or-less right).

This oddity is visible on Pike 7.8.700 on Windows and 8.0.1 on Linux.

Is this a bug, or am I misunderstanding this_program?

ChrisA