Invitation Update fails on OX App Suite with Thunderbird

Hi,

we have some troubles with updating events via caldav. Currently installed versions:

UCS: 4.4-1 errata273
OX App Suite: 7.10.2-ucs1

As client, we are using Thunderbird with Lightning. Joining all calendars with Caldav into Lightning - this works quite well.

Problem description and workflow:
We create a event in Thunderbird, invite an external Mail address and save it into the caldav calendar. After accepting the invitation from the mail address, we click on “update” on Thunderbird to update the event with the “accept/deny/…” from the other mail address. After clicking update, a error comes up:

2019-10-10_14-24

On the server, this error is shown by the apache2 process:

- - - [10/Oct/2019:14:24:44 +0200] "PUT /caldav/Y2FsOi8vMC84MQ/a961391b-121c-4149-95ba-854e51b327c3.ics HTTP/1.1" 403 355 "-" "Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 Lightning/6.2.7.2"

So this is a default configuration and standard installation. What can I do, to solve this behaviour? If I accept it in the web interface, everything works fine. Error 403 as web code is a “permission denied”.

Thank you very much,
Ludwig

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