Here is an example.

 static_page_id |          filename           | folder_id | show_comments_p
----------------+-----------------------------+-----------+-----------------
           2475 | /static1.html               |      2472 | t
           2478 | /static-folder/static1.html |      2477 | t
(2 rows)

static_page_id 2478 is supposed to be deleted. It lives in static_folder 2477. Here is what I am getting in the log:

[23/Oct/2001:05:41:47][771.8197][-conn1-] Notice: Querying 'select __exec_6_del
ete_old_files ();'
NOTICE:  ***Deleting id:2478
NOTICE:  *** Number of rows deleted: 1
NOTICE:  Deleting symlinks...
NOTICE:  Unscheduling item...
NOTICE:  Deleting associated revisions...
NOTICE:  Deleting associated item templates...
NOTICE:  Deleting item relationships...
NOTICE:  Deleting child relationships...
NOTICE:  Deleting parent relationships...
NOTICE:  Deleting associated permissions...
NOTICE:  Deleting keyword associations...
NOTICE:  Deleting associated comments...
NOTICE:  identifier "journal_entry__delete_for_object" will be truncated to "jo
urnal_entry__delete_for_objec"
NOTICE:  Deleting content item...
[23/Oct/2001:05:41:47][771.8197][-conn1-] Error: Ns_PgExec: result status: 7 message: ERROR:  -20000: 
Folder ID 2477 (/static-folder) cannot be deleted because it is not empty.

So it looks like performing both these deletes in the same function is causing the problem.