Description
On a stateless page, feedback added in onSubmit is not displayed because the FeedbackPanel collects its feedbackmessages prior to onSubmit being called. This is a regression since 8.0.0-M8, caused by https://github.com/apache/wicket/commit/c27a57b31a0e519ef15dfe08b425d85f9a24f685 (for WICKET-6503).
I'll add a testcase to show the problem.