Thank you, very much for the second link.
What is weird is that if my dbLoader writes the source to a file then returns a filehandle (the method used in the test) to that file both 'works.pl' and 'worksnot.pl' run successfully. But if dbLoader opens a filehandle on the reference to a string (aka in-memory-file) only 'works.pl' runs successful. 'worksnot.pl' still throws the error shown in the op.
Apparently I'm looking in the wrong place for the source of the problem. If dbloader opens a filehandle on an in-memory file where the contents are copied (rather than on the reference returned by the database) all is well. ie:
open my $fh,'<',$body_sref
or die "Couldn't open '\$body_ref' for reading. $!";
open my $fh,'<',\(my $buffer=$$body_sref)
or die "Couldn't open in-memory file for io. $!";