The date pickers currently open with today's date selected. If you click on today's date the date is selected. If you click on the date, it deselects the date closing the date picker and removing the current value if it exists.
New users at our firm intuitively want to click on a date, so when they click on today's date, it simply enters in no date as the date is already selected.
Suggestions:
1) Don't auto close the date picker without a selected date
2) Don't auto suggest today's day (but still open date picker to current month)
3) Don't close date picker when clicking on a date and always require users to click the OK button.