Can you check and test the ThemeShadowChrome function with slide animation?
I use the ThemeShadowChrome container in ComboBox sytle,when set the popup Animation for Slide,As follows: <Popup x:Name="PART_Popup" Placement="Bottom" PopupAnimation="Slide"> The animation effect start position is from the ComboBox's left top,instead of from the left bottom, when don't using the ThemeShadowChrome container,the animation effect start position is from the left bottom,it is OK!
sorry ,the xaml code can't show,the comboBox's popup style like the follows: Popup x:Name="PART_Popup" Placement="Bottom" PopupAnimation="Slide"
Thanks for reporting. Unfortunately until a solution is found I guess we'll have to stick with either fade animation or without the theme shadow.