WPF AutoCompleteBox Popup doesnt close on click of a button But it hangs

DropDown Displays the List of Content but on click of Search Button, we have a functionality of Windows to disappear and reappear, While in this phase the dropdown(popup) hangs.

Aim is when clicked on Search Button, the DropDown should disappear.

I have tried IsDropDownOpen = false; in RadButton_MouseLeftButtonDown RadButton_PreviewMouseLeftButtonDown

but it didnt work.