Problem sharing calendars to groups

I am running on Nextcloud 10.0.3 using the calendar app 1.4.1.
(Debian 8 64bit - virtual machine running on VMWare)

I made Special Groups for sharing different calendars. E.g. group1 is for all users of calendar1.
If i share my calendar1 to all users participating group1 saying yes for editing everybody should make entries in it!?
Except me as the owner of calendar1 nobody can insert any entries to calendar1.
I also tried sharing directly to Special users instead of Groups with the same issue.

Few month ago using owncloud i had no Problems with that.

Does anyone have an idea on this? Is there any option or app i have to install/configure?

Thank you for ideas …