It might not look like it, but the HeaderDateFormat is applied correctly in this case (to the top-most scheduler header). In prior versions it was used to format the column headers instead of ColumnHeaderDateFormat.
You should be able to achieve the same result (in both Week and Timeline view) by using:
We're aware of the appointment misalignment issue and we're currently working to resolve it. We'll post a message here when we're ready with the fix.
the Telerik team