Expression Editor Window Suggestion (or bug?)

When I click on a measure I get the Expression Editor window appearing, as I would expect. However, when I click on another measure, I don't get another Expression Editor window, as I would expect. The new selected measure simply replaces the contents of the existing Expression Editor window. I realize I can go back and forth between my measures using the arrows in the upper right of the editor window but I really would expect another Expression Editor window to appear. In fact, I haven't found a way to actually get a second Expression Editor window to appear. Maybe I can't?