[kronolith] accepting invitations does not add them to the calendar

[Calendar Debug]

Hello,

I'm testing a horde webmail groupware installation and it seems that
events are not added to the attendees' calendars when clicking on the
"accept and update in my calendar" -> Go button.

The scenario is:

initiator:
- creates event in Horde UI
- adding attendee; attendee Free/busy shown as green;  green box "the
notification was successfully sent"
- receives email about event being added (notification)
- event is shown in the initiator's calendar

attendee:
- "accept and update in my calendar"-> Go; the UI says "the event was
updated in your calendar"; "reply sent"
- the event is NOT added to the attendee's calendar

initiator:
- receives email from attendee about the invitation being accepted
- clicks on "update respondent status"; green box "respondent status
updated"
- editing the event -> "attendees" tab shows the attendee with status
"accepted" (checked) BUT the free/busy is still green - probably because
the event has not been added in the attendee's calendar.

Both users have full permissions on each others calendars. The interface
is dynamic.

Please let me know if I'm missing something very obvious...

Thank you for your help!

Horde 5.0.4
Imp 6.0.4
Kronolith 4.0.4
Centos6.3