Localized date not sanitized

[dpaleino]

Hello,
Magento 2.1.7. In /admin/admin/system_design/new/ , I have two datepickers, which correctly show me localized month names, and date format (for Italy, that's dd/mm/yyyy). Clicking a date for the popup correctly populates the input field with the localized format.

As soon as I click Save, I get:

Exception #0 (Exception): Invalid input date format '31/12/2017'

Going back, and manually inputting the date in the mm/dd/yyyy format correctly saves it (and then, in the grid, it shows up with the correct localized format)

Here's the first few lines of the backtrace:

Exception #0 (Exception): Invalid input date format '31/12/2017'
#0 /home/dp/magento2/vendor/magento/zendframework1/library/Zend/Filter.php(114): Magento\Framework\Stdlib\DateTime\Filter\Date->filter('31/12/2017')
#1 /home/dp/magento2/vendor/magento/zendframework1/library/Zend/Filter/Input.php(722): Zend_Filter->filter('31/12/2017')
#2 /home/dp/magento2/vendor/magento/zendframework1/library/Zend/Filter/Input.php(701): Zend_Filter_Input->_filterRule(Array)
#3 /home/dp/magento2/vendor/magento/zendframework1/library/Zend/Filter/Input.php(785): Zend_Filter_Input->_filter()
#4 /home/dp/magento2/vendor/magento/zendframework1/library/Zend/Filter/Input.php(381): Zend_Filter_Input->_process()
#5 /home/dp/magento2/vendor/magento/module-backend/Controller/Adminhtml/System/Design/Save.php(24): Zend_Filter_Input->getUnescaped()
#6 /home/dp/magento2/vendor/magento/module-backend/Controller/Adminhtml/System/Design/Save.php(38): Magento\Backend\Controller\Adminhtml\System\Design\Save->_filterPostData(Array)

[magento-engcom-team]

Duplicate of #10580