Meeting invitations on Android

i’m evaluating ucs with Open App Suite and got a problem / question regarding meeting schedules and invitations.
I setup a Android Phone with emails over imap and calendar and contacts with DAVx5. All running good so far.

When i create a new calendar entry on the web an email is send to the attendee, also good so far. On the web i can accept this invite but on android there is no option to accept the invite, only a link to the calendar entry on the webinterface where i have to login.

When i open the calendar entry on the android phone i have the buttons to answer the invite, but not in the invite mail.

Is this the normal behaviour of the system?