Steps to reproduce:
1. Set your client operating system timezone to Australia/Melbourne
2. Set timezone to Auto or Australia/Melbourne in Roundcube
3. Go to Calendar and create an event on Sunday 18:00-19:00
4. Refresh the page and see the created event is missing.
More at https://issues.kolab.org/show_bug.cgi?id=5190
OTRS#1012160