cross-linking the android bug: android-bug
I agree davdroid can’t do anything here. Some background:
I think this is because in the EventInfoManager, /src/com/android/calendar/EventInfoFragment.java#L888
the status is set to Attendees.ATTENDEE_STATUS_NONE by default (originally part of the AttendeesColumns), which points to the same constant value as STATUS_TENTATIVE for the STATUS field.
So whoever designed this, not only set ATTENDEE_STATUS_NONE == STATUS_TENTATIVE = 0, but also got confused which field to save for Attendee and which belongs to the eventStatus field of the Event. (Great Programmer 😣 )
Means: everytime an event that has eventStatus = NULL is edited, it will be overwritten with eventStatus = 0 (which means tentative!)