'Simplify node form' breaks 'File attachments'

When the 'Simplify node form' option is enabled and the 'File attachments' fieldset from the upload module is in the 'Advanced options' fieldset, attempting to attach a file will result in the error: "Validation error, please try again. If this error persists, please contact the site administrator."

There appears to be a similar issue with the CCK Fieldgroup Tabs module, which appears to perform a similar function, moving the fieldsets into tabs rather than another fieldset: http://drupal.org/node/370233. So I'm guessing it could be an issue with the upload module as much as with form filter.

Disabling the 'Simplify node form' option or adding the 'File attachments' fieldset to the exclusion list in formfilter_ui.module resolves the issue, but is less than ideal since the 'File attachments' fieldset is no longer contained in 'Advanced options'.