My fault. I failed to keep into consideration that you upgraded to Custom Properties for Joomla 1.5.
This version of CP has only the date-range-search "event mode"
That is a very specialized search that considers the creation date of the article as the beginning of the event, and end publishing date as the end of the event.
The following example explains why you can't enter a date before today.
Let's assume that there's no date validity check.
You have one event that starts the first of January 2013 (created date 1st of Jan) and ends the 31st of July 2013 (end publishing 31st Jul).
You search for events from the 1st of July onward. The event is returned among the results, because its ending is past the search date.
2013-01-01|------------event-------------------|2013-07-31
^-------------2013-07-01----date from
------------------------------------------------today------^
The problem is that if you click on the article you get an error from Joomla, because the
end publishing date is earlier than today. In other words, you are trying to open an already expired article.
So, instead of having CP to return articles that can't be opened, we prevent this problem to happen by forcing the dates to be past today.
