Drupal CKEditor fails to load in RichTextEditor custom fields

When using Drupal default editor (CKEditor) as RichTextEditor,
the toolbar does not get loaded in Custom Fields of type RichTextEditor (and the info about filter_html / full_html / plain_html are all three displayed)
Firebug raises error on ckeditor.js line 126 p is null

The wysiwyg editor is working perfectly everywhere else
Having the the fields set initiatially collapsed or not does not make any change
Having the the fields set integrated or tabbed does not make any change

Any clue ?
Thanks

CiviCRM with Drupal7