Comment 8 for bug 133541

Looks like this was fixed upstream as 554962 rather than 468075.
http://svn.gnome.org/viewvc/gnome-control-center?view=revision&revision=9038
http://bugzilla.gnome.org/show_bug.cgi?id=554962

A workaround for me was to use gconf-editor to set /apps/metacity/general/action_double_click_titlebar (and action_middle_click_titlebar) to "toggle_maximize_vertically" instead of "toggle_maximize_vert".