I found that refreshing a submitted form results in processing the form data again. In some other CMS's I've used, repeated submission pops up a warning (e.g. "You have already submitted this form, are you sure you want to submit it again?").
What's the right way to address such cases in Orchard? I.e. prevent repeated processing of form contents, and/or warn about repeated submission.
@BertrandLeRoy confirms that redirect after submission is the correct way to handle this case in Orchard. Thanks!