Right click on the panel, go to "+ Add applets to the panel". The applet, "Grouped window list" should be removed, it is the one that adds the grouping that annoys both of us. You then need to add the applet, "Window list" to get the old way back.
FWIW when I did this it worked the old way but the spacing was very broken. Between the menu and the window list there was a big gap, I reduced it by adding the "spacer" applet, but only somewhat. The quicklaunch icons are to the left of the window list now too, can't figure out how to fix this one....yet. In any case it is annoying but still far better than the Windows X inspired annoyance.