In my app, I've added some On_Validate logic to prevent users from changing a date field to a day that is "off", i.e. Sunday or Holiday.

However, in the Calendar report, users can drag any appointment to those days.

In other words, the On Validate script seems to only fire when the record is opened for editing. In the Calendar view, the date field gets updated. I could write the code for the "OnUpdate" event but by then, the data has already changed. Also, I don't not have access to the old date value.

Is this by design? an oversight? How can I prevent users from changing the dates to illegal values?