CiviCRM session instance not working when Masquerading in Drupal 7

Have just upgraded to D7-5.20.1 and noticed that CRM_Core_Session::singleton() does not work when masquerading.

Setting a breakpoint in a Drupal page while masquerading and running Civi::log()->debug(var_export(CRM_Core_Session::singleton(),true))

Results in the following in the log:

Dec 11 13:08:57  [debug] CRM_Core_Session::__set_state(array(
   '_key' => 'CiviCRM',
   '_session' => 
  array (
    'masquerading' => '76',
  ),
))

Edited Dec 12, 2019 by Michael McAndrew

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