Inconsistent handling of case type causing fatal error when creating new case

Apr 12 10:41:55 [info] $Fatal Error Details = Array
(
[message] => We experienced an unexpected error. Please post a detailed description and the backtrace on the CiviCRM forums: http://forum.civicrm.org/
[code] =>
)

Apr 12 10:41:55 [info] $backTrace = <site_url>/CRM/Core/Error.php, backtrace, 260
<site_url>/CRM/Case/XMLProcessor/Process.php, fatal, 460
<site_url>/CRM/Case/XMLProcessor/Process.php, getMaxInstance, 300
<site_url>/CRM/Case/XMLProcessor/Process.php, isActivityPresent, 419
<site_url>/CRM/Case/XMLProcessor/Process.php, createActivity, 140
<site_url>/CRM/Case/XMLProcessor/Process.php, processStandardTimeline, 116
<site_url>/CRM/Case/XMLProcessor/Process.php, process, 58
<site_url>/CRM/Case/Form/Activity/OpenCase.php, run, 292
<site_url>/CRM/Case/Form/Case.php(355) : eval()'d code, endPostProcess, 1
<site_url>/CRM/Case/Form/Case.php, eval, 355
<site_url>/CRM/Core/Form.php, postProcess, 250
<site_url>/CRM/Core/QuickForm/Action/Upload.php, mainProcess, 153
<site_url>/CRM/Core/QuickForm/Action/Upload.php, realPerform, 130
<site_url>/packages/HTML/QuickForm/Controller.php, perform, 203
<site_url>/packages/HTML/QuickForm/Page.php, handle, 103
<site_url>/CRM/Core/Controller.php, handle, 277
<site_url>/CRM/Case/Page/Tab.php, run, 161
<site_url>/CRM/Case/Page/Tab.php, edit, 193
<site_url>/CRM/Core/Invoke.php, run, 213
<site_url>/drupal/civicrm.module, invoke, 350

Some debugging indicates that normally the case type "Referral to Non-HS Counselor" gets passed into XMLProcessor::retrieve() most of the time as

"referral_to_non-hs_counselor"

but is being passed in here as

"Referral to non-HS counselor"