thanks so much for answering david
right now i'm using the "editor" element, although for section images i also want to include "filemanager" and will probably run into the same problem.
currently i'm not preparing the "editor" element, just doing the steps to save the uploaded files (file_save_draft_area_files) - so it is possible this step fails if the editor element was not prepared correctly? i figured new input would still be correctly saved, and wanted to take care of preparation later.
i'm aware of the documentation, but it's more complicated since i'm not doing it in a normal moodle form, but in a course format plugin.
anyways thanks for the input, i ll try to include the preparation step and if i get it to work i ll be sure to post it here for the benefit of others who might run into the same trouble