After submitting a query, you always had to confirm the query plan (and you also had the possibility to edit it directly, before confirming). This functionality is now switched off, because it caused problems with the session management. You can still view the full query plan in the Job overview tab, in the bottom section Query Plan. But you cannot edit it manually before query submission anymore.
If you discover a bug in a query plan, please contact us or submit your issue directly to the PaQu issue list at GitHub.