[Quantum7]

Steps:
1. I create an appointment (10-12-2007).
2. I set begin date to 21-12-2007.

Now, why doesn't end date also go to 21-12-2007? What's the point of having an end date in the past? Also even if there would be a hypothetical situation in which that would be desirable, in 99.99% of the situation's it wouldn't.

Suggestion:
If the end date is smaller than the begin date, automatically set the value of the end date to the same value as the begin date.

Note: This might require the "calculated attributes feature"

Also, same suggestion for begin time / end time.