Hi Jan!
I cannot reproduce the problem through on either my local site with Moodle 3.6 RC1. There may be some other error on your site that triggers this problem, please check your web server logs for errors, and enable debugging in Moodle to see if you get any errors displayed.
You can also try it on https://demo.moodle.net and share more detailed step-by-step instructions to reproduce it
Cheers!
Sara