Recurrent all day events cannot be modified

At least not single instances of them.

There is no error message, it is just after editing them and submitting the form, the current calendar month reloads and shows the event in the old date.

The reason is that the update backend uses addObjectFromRequest and as the date is submitted without time, the modification object does not get created.

The (very clumsy) workaround is to manually type in a 00:00 behind the date in the start/end date fields.