Why does my current lister disappear when I open a new one?

I have a lister that is open (it's one of my saved listers). If I open another saved lister, the current one disappears and the new one opens. Why can't I just open multiple ones? What is doing this?

Go to the list of Layouts in Preferences, select the layout and turn off "close all existing listers when loading this layout".

Thanks leo! I've been meaning to ask that for like a year now, but never got around to it!