preg_match() expects parameter 2 to be string instead array

Hi, I'm getting this error after saving new edit of nodes that previously had a different node path setting.
Example:
* My node-type 'events' had the path 'news/[title-raw]' --
* I created a number of events which set a path based on that pattern.
* Then I changed the pattern to 'events/[title-raw]'
* My update action (in General settings) is: Create a new alias. Delete the old alias.
* So I have to re-edit each node to save the new path...
* As expected, when I edit those existing nodes, the path is changed after saving.
* But I get this error message:

warning: preg_match() expects parameter 2 to be string, array given in MYSITEPATH/includes/bootstrap.inc on line 723.

Have you seen this before? It's very troubling because every subsequent save of those nodes returns the same error.

Actually - creating new nodes of that type return the same error as well... I'm not sure what to make of it. Creating or saving other node-types don't return an error.

I wish the error were less ambiguous ;)

Here's the first place I added the issue, because the same error was present: http://drupal.org/node/314032#comment-1047832

Hope this helps track it down. Cheers!
Scott