Confusing date formats

Date formats

1)
field page -> custom code

you get Y-m-d from $data

2)
in a custom button , server event
you get from a $data = $button->getCurrentRecord();
the language format of the misc. page

for german :
d.m.Y

3)
Search box works only with Y-m-d

How I can change this, for my german customers ? Should it not be like defined on the misc. page ?

Is this a bug ? I need help