Tested in FF and Chrome on demo.contao.org -
Enter an invalid date in datepicker field (eg Members DOB field or SiteStructure Publish to/from fields)
and the error throws the datepicker icon out of its position.
Although it is still usable in the demo site, for some reason it is not in my modules (it will not trigger in the new position)
Correctly insert the date picker in the DOM tree (see #4158)
Fixed in 47bf665.