Caldav sync Lightning: Problems with Private Appointments

Hi there,
i just started collaborating with NextCloud and must say it is just great! Thank you so much.
One issue i have:

Admin created a calendar for User A. The calendar ist read/write for user A and read only for user B.
When integrated in Lightning, a private Appointment of User A is readable for User B. When using the web interface, it is labeled as busy. The same using the ios calendar feature.
I also tried it for User A creating a calendar… but still no luck.
Can anyone help me out here? Do you need any more information?

Thanks a lot,
julian

please create a bug report at https://github.com/nextcloud/server/issues

feel free to mention me