As almut already told you there is no clean straight forward solution.

These kind of problems normally originate from trying to use a reference as hash key...there are moduls with specially tied hashes to handle this.

Their basic solution is to memorize the relation in a look-up-table, whenever a stringification is needed.

$ref_of{$stringification}=$reference;

Keep in mind that the refcounter is automatically incremented as long as the table entry exists, this could lead to new problems if you don't take care about memory consumption...