Upon changing the DAV link, Akonadi shows the new link in the GUI, but if there are events added to the calendar between the last sync and the link change, it still tries to use the old link (and inevitably fails).
Could you expand a bit more: where are the events added? On the server? A step-by-step to reproduce the bug would help.
This bug has only been reported for versions older than KDEPIM 4.14 (at most akonadi-1.3). Can anyone tell if this bug still present? If noone confirms this bug for a recent version of akonadi (part of KDE Applications 15.08 or later), it gets closed in about three months.
Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.0 aka 15.08), please open a new one unless it already exists. Thank you for all your input.