%*ENV and 'use' strange behaviour

$ cat testenv.pm6

print 'Test existence of %*ENV<PERL6LIB>: ';
print %*ENV.exists('PERL6LIB');
say " OK, still alive";

$ rakudo testenv.pm6

Test existence of %*ENV<PERL6LIB>: Bool::True OK, still alive

$ rakudo -e 'use testenv'

Test existence of %*ENV<PERL6LIB>: Method 'exists' not found for invocant of class 'Failure'
  in main program body at line 2:testlib.pm6