I replaced the main view by a user-defined view. It contains a Job grid with 2 columns.
How to reproduce:
In the Job grid start a job by clicking the 'Schedule a build' button next right to the job.
1. The job is started without complaints.
2. The job overview page is still shown.
I get the error 'You must use POST method to trigger builds. (From scripts you may instead pass a per-project authentication token, or authenticate with your API token.) If you see this page, it may be because a plugin offered a GET link; file a bug report for that plugin.'
After clicking the 'Proceed' button the job is started. Then I get an empty page shown and have to click the 'Back' button in my browser to return to the Job overview page.