The sed script in glib/Makefile.am that is supposed to paste in the python interpreter path into gtester-report is broken. The regexp match is for:

-e '1,1s|#!/usr/bin/env python\([0-9]\+\(\.[0-9]\+\)\?\)\?|#!${PYTHON}|' \

but gtester-report begins:

#! /usr/bin/env python

There's differnce of a whitespace after the shbang, which prevents the regexp from matching and therefore the installed gtester-report script still specifies:

#! /usr/bin/env python

instead of whatever PYTHON was determined during ./configure