Event editing: checkbox for date span does not stay checked

Summary

When re-editing an event with date span, the corresponding checkbox is not checked.

Steps to reproduce

Create An Event with a date span. Edit that existing event.

What is the current bug behavior?

The date span checkbox is not checked; the end date is hidden.

What is the expected correct behavior?

The checkbox should be checked if a date span was selected before. The end date should then be visible of course.

Relevant error messages and/or screenshots

none

Possible fixes

Change the UI behavior.