You got it right, this only happens to events created in the 3.7 version, and NOT with new events created with version 3.8.
Whenever I try to edit these events (in 3.8) as single events, I am asked about breaking the event out (again). This has no effect thou. In the edit event screen it still says: “You are currently editing all events in a recurring series.”
The textual contents of the events are still different from the original recurring event thou.