Currently the only point where the POST_PERSIST Event will be fired is in UploadCotroller::upload(). If you're using an Orphanage you have to manually call the Orphanage::uploadFiles method. In addition, the PostPersistEvent always gets a Request object, which is not really useful when using the Orphanage.

Either create a new Event which will be fired after the files where successfully uploaded by the Orphanage or move the request parameter to an option array, like in PostUploadEvent.