"Create Event" dialog shows selction of calendars from main wiki even in subwikis, if extension is installed on all subwikis

as in the description:

• setup a XXiki instance with both a main and a subwiki
• install the MoccaCalendar on all wikis
• in the subwiki, create a second calendar (ans maybe on the main wiki, too, but with a different name
• go to the start page of the subwiki's MoccaCalendat and click "Create new Event"
  (or click into an empty space on the calendar widget)

Expected behavior:

• the first selection allows to select a calendar from the subwiki

Actual behavior:

• the first selection allow to select calendars form the main wiki instead
• selection a calendar which only exists in the main wiki creates an event in the subwiki, but with a non-existing parent with the name of the calendar in the main wiki.