Unexpected behavior of web IDE when trying to create a MR for projects without write access

When editing things on projects without write access in the web IDE it shows that one does not have write permissions for the master branch and suggests to create a different branch instead:

I thought it will create that branch in my fork or create a fork when none is available. However, that does not seem to be the case.

When hitting the commit button, the following error message appears for me:

I don't know whether this is considered a bug. As a feature request I'd suggest to show a more useful message and ideally make the user experience more seamless by directly offering to create a fork or commit to the existing fork.