witch file is triggerd to make sure logon screen's background is changed

Hi there,

I like to know wich file is triggerd by variety to make sure the logon window's wallpapper is changed, because it seems elementary os has changed the way to display the background image and variatys Option to change the Wallpaper at the start doesn't work anymore in elementary os 0.4.

Could you tell me with file is changed by variaty when marking this option as aktive so I can drop them a note!

Thank you!