New filetype selector shows file type .xxx which is reserved for unknown file type mapping

Create an assignment and a workshop. Edit settings for each and under 'Submission types' click the 'Choose' button Confirm that You don't see the 'xxx' type listed. Close the dialog and type in '.xxx .html' in the field instead (space separated) Submit the form and Confirm that you see a validation error stating that only the .xxx extension is invalid.