I haven't got the N9 yet, but I had a similar bug on the N900. With UK language and Netherlands time, and a sync with Exchange, all day events were shifted by an hour (UK time? Winter time?) After changing, events could shift a day until I no longer knew what the original date was. Seems to me that the sync protocol has no "All day" tag but only a start and end time. Stopped using all day events all together.