is_planar( ) produces random results

[gwselke]

For some planar graphs at least, is_planar( ) randomly yields true or false.

Here is code to reproduce:

#! /usr/bin/perl
use v5.32.0;
use Graph::Undirected;
# use GraphViz2;
my $g = Graph::Undirected->new( );
$g->add_weighted_edge( 'J', 'S', 21);
$g->add_weighted_edge( 'F', 'M', 11);
$g->add_weighted_edge( 'F', 'H', 11);
$g->add_weighted_edge( 'J', 'T', 14);
$g->add_weighted_edge( 'T', 'G', 14);
$g->add_weighted_edge( 'T', 'S', 13);
$g->add_weighted_edge( 'G', 'S', 5);
$g->add_weighted_edge( 'G', 'H', 8);
$g->add_weighted_edge( 'G', 'M', 17);
$g->add_weighted_edge( 'S', 'H', 11);

for my $i(0..9) {
  say 'Graph is ', $g->is_planar( ) ? 'planar' : 'not planar';
}
# my $gv = GraphViz2->from_graph($g);
# $gv->run( 'format'=>'png', output_file=>'f.png' );

And here is one result (exact distribution will vary from call to call):

Graph is planar
Graph is planar
Graph is planar
Graph is planar
Graph is planar
Graph is not planar
Graph is planar
Graph is not planar
Graph is not planar
Graph is not planar

In fact, the graph is clearly planar, as can be seen from the enclosed diagram (produced by uncommenting the GraphViz-related lines in the code above).
I have tested on Windows 10, Perl 5.42.0, Graph 0.9735