When Private Upload is enabled, options to delete and list file attachment disappear

[ Setup: Drupal 6.22, all modules up to date, OSX ]

When I enable the Private Upload module, the file attachment interface changes.
The 'delete' and 'list' checkboxes for file attachments disappear.

I'm not actually sure how to categorize this issue.

I can attach a file, but the resulting file name shows the path as: http://mysite.local/system/files/private/mypic.jpg [ note 'system' ]
actually the file is here: http://mysite.local/sites/mysite.local/files/private/mypic.jpg

The attachment is followed by two checkboxes, a popup with what looks like weights (-1,0,1) and another checkbox - all vertically.
Further attachments are each followed by the same set of widgets - only the range in the popup increases.

And - there is no more option to 'delete' or 'list' attachments.

I am using Private Upload because Webform Protected Download requires it, but I'm getting this issue just with 'regular' content types (e.g., Page).
I can reproducibly get the issue to go away by disabling Private Upload.
Then the file path once again looks correct and the 'delete' and 'list' checkboxes re-appear.

If I edit the page, the following message appears, I don't know if it's relevant:
warning: Parameter 1 to theme_private_upload_form() expected to be a reference, value given in /Library/WebServer/Documents/gallery6-drupal-6.22/includes/theme.inc on line 668.

When I save the page, the following message appears:
warning: function_exists() expects parameter 1 to be string, array given in /Library/WebServer/Documents/mysite/includes/form.inc on line 770.

Private upload status reports all is well:
Public File Folder: 'sites/mysite.local/files'
Private File Folder: 'sites/mysite.local/files/private'
sites/mysite.local/files/private exists and is writable. Great.
You have an .htaccess file in private folder. Great.
Your private folder is not accessable. Great!
File download method is set to public. Great.
There are no old-style private files hanging around. Great.
There are 1 files in the private folder, and the DB thinks there are 1 private files. Great.
There are no public files attached to private nodes. Great.
Uploaded files in db: 1 files attached to 1 nodes.

I've tried this as admin (with all privileges) as well as auth. user. Same result.
Also tried different themes (Marvin and Garland).