Some panels (Background, Sound, Printers) cause the sidebar to disappear when visited
This is with master (2520aea6). libhandy is at 607152c2d1abd3270ba8896dbb823bc2b7534c19.
Some of the panels cause the sidebar to disappear. When this happens a critical is shown:
(gnome-control-center:8242): Gtk-CRITICAL **: 10:18:55.668: gtk_widget_draw: assertion '!widget->priv->alloc_needed' failed
(didn't get a backtrace of that, can if you want). See this screencast - hopefully it's obvious what the problem is: