Lots of bugs with the validation. Try to list all I found.

Okay, I've found a few bugs with the validation. I tried to test them and will list them as clearly as I can.
These first few aren't really to do with validation, but they're here for you anyway.

#1 Date Format appears twice for Text Field with jquery pop-up calendar

"Format: 2008-06-05 Format: 2008-06-05" appears below the text field.
See image 1-1.png

#2 Date Format text not needed for select lists

"Format: 2008-06-05" appears below select lists when it is not needed. (save possibly when Position of date part labels is set to none
See image 2-1.png

#3 Within option isn't documented correctly for textfields

Either that or it doesn't function as desired. Docmentation below the Position of date part labels section states "'Within' will insert the label as the first option in the select list and in blank textfields."
Nothing appears in the text fields.

#4 PHP Warning error for date_formatter_process()

On validation, preview AND submission, PHP warning errors are generated for date_formatter_process(). See image 4-1.png

The problem lies in that the function requires more variables:

function date_formatter_process($field, $item, $node, $formatter = 'default'){...

//and this is what is supplied
$dates = date_formatter_process($element);

Validation errors with select lists

#5 Position of date part label: Above

After validation, the date part labels appear, but do not say for which field. This could pose a problem if you have multiple date fields. See image 5-1.png
After validation, blank is no longer an option which then selects the first date available in the list. See image 5-2.png
After validation, blank fields are not hilighted in red as they should be. See image 5-2.png

#6 Position of date part label: Within

After validation, the date part labels do not appear nor does it say for which field. See image 6-1.png
After validation, blank fields are not hilighted in red as they should be. See image 5-2.png

#7 Position of date part label: None

After validation, the date part labels do not appear nor does it say for which field. See image 6-1.png
After validation, blank is no longer an option which then selects the first date available in the list. See image 5-2.png
After validation, blank fields are not hilighted in red as they should be. See image 5-2.png

These are all the errors I found while going through this quickly. You've probably noticed them, at the very least, the php warning, but I thought I would try to be as helpful as I can.
Let me know if there is any other information you need for me, or anything I can do.