Refusing group application doesn't work

Summary

I'm "admin"/responsible of a working group ("Arbeitsgruppe"/"AG") and I couldn't refuse an application for this group.

Steps to reproduce

1. Be the admin of a working group.
2. Have an application.
3. Try to refuse/reject it.

What is the current bug behavior?

By clicking the refuse button for an applying person, the message for handling the input [click] shows up, but the application is still active/waiting for a response. Accepting the application and kicking the person by editing the group member list works as expected.

What is the expected correct behavior?

Deletion of the application with a refuse/rejection message for the applicant.

Possible fixes

It seems that there's missed a link to the code or just the piece of code itself that executes the rejection.