Error: Key Exists / OptionWidgets.module / Nodereference - editing referenced c-types

I searched the issue queue and didn't see anything that I could tell was similar so I'm posting this in hopes to provide the devs with more info/feedback.

Here is the error message:

warning: array_key_exists() [function.array-key-exists]: The first argument should be either a string or an integer in /Users/jamm/Sites/drupal-6.1/sites/all/modules/cck/optionwidgets.module on line 319.

When I created content-type X, I added a few fields including a nodereference select-list field ID {not required, unlimited, referenced content-types none}. I didn't choose the referenced content-type yet because I hadn't created it yet. After creating the desired reference content-type Y, I returned to field ID, selected content-type Y for referenced content-type, added some verbiage to the help text, and saved the field. Upon returning to 'admin/content/node-type/X/fields' I received the error message above. Immediately after, I returned to 'admin/content/node-type/X/fields/field_ID/edit' to see if the previously added settings were lost.

To my surprise, the settings were saved even though I received the error.

Background Info:

Local MAMP

Apache 2.0.59
MySQL 5.0.41
PHP 5.2.3

Drupal 6.1 (Clean Install)

CCK 6.x-1.x-dev (2008-Mar-15)
Contemplate 6.x-0.4-2
Devel 6.x-1.6
Views 6.x-2.0-alpha2