Date format of date shopper field in cart

[Three_d]

Hello I use VirtueMart 2.0.18.
I've made a new "shopper field" with the "Field type" "Date".
Then I changed at the "Language Manager" of Joomla at the "Overrides" tab the "Language Constant" "COM_VIRTUEMART_DATE_FORMAT_INPUT_J16" to d-m-yy (this gives for example: 18-01-2012).
When I go to the frontend and add the client information then the date format is good in the screen where you add the date with a datapicker.
But when I go back to the cart where al the selected products are I see the date format in yy-m-d format (for example: 2012-01-18).
See attached file.

How can I change this format to d-m-yy ?

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