I'd try replacing $Config{cc} = "$^X $Config{cc}"; with $Config{cc} = $^X . ' ' . $Config{cc};

Doesn't help, unfortunately. It was also suggested I try making $Config{cc} local to that test script, but that changes nothing.

Does it work if you load some other inconsequential module; say bytes or less or maybe just strict?

Nup - has to be 'blib'. The script already loads strict.pm, and I did try out 'less' and 'bytes' ... to no avail. (There may of course be some module other than 'blib' that has the same effect.)

I probably ought to take a look at blib and see what it's doing. Perhaps, therein, lies the clue.

Cheers,
Rob