When editing a source, or editing a family (and possibly elsewhere too), added notes, shared notes, multimedia objects, and restrictions are added at the wrong level. This can result in unwanted facts being created with the added note.
See SVN6906 edit_interface.php lines 1154-1158 and 2660-2664. The calls to print_add_layer do not specify a level. It should be 1, but the function defaults to 2. That results in an unwanted level 1 record being created to hold the incorrect level 2 record.
IMO, the print_add_layer function (in includes/functions/functions_edit.php) should not have a default for the level and that all calls to this function should be reviewed and an explicit level set for each call. If uncertain, it can be set to 2 as per the current default. AFAICT, files that refer to print_add_layer are: