Calendar Buttons not displayed

Hello,

I just noticed that when I send a calendar invite from webapp the recipient gets the email but no invitation…

It looks like this ( I checked in gmail too, if I send it there):

When: Friday 21st April 2017 15:00 - Friday 21st April 2017 15:30
Where:

~~~~~~~~~

But nothing where it can be accepted.

I can see the behaviour either internally (if I send the invite to another webapp user) or externally, if I do it to gmail.

These are the versions of the software I am using:

WebApp:
3.3.0.582-421.1
Kopano Core:
8.3.0-500
Z-Push:
2.3.5+0

Am I doing something wrong?

This appears to be fixed in 8.4 or perhaps it was already fixed in a later version than the build I was using.