Forum .LRN Q&A: not returning to using calendar-portlet after adding an event

Not sure why this is like it is, but when you add an event it is the calendar-package (cal-item-new) that takes care of this. If you then click on List|Day|Week|Month view you are still in calendar-package and only you own events are shown.
If you click on Calendar-link in the menu the calendar-portlet is used and all events are again shown.

Is this a feature or an bug?

It's a "feature".

This is due to unclear integration between portlets and applications, and isn't going to be trivial to fix, unfortunately.