CPU eaten alive as countless sizing operations occur (Allocating size to GcalEventWidget without calling gtk_widget_get_preferred_width/height() )

The git version eats 50% of my CPU through Xorg. While running, thousands of occurrences of this message (with the "0x41387a0" part changing) happen continously:

(gnome-calendar:4973): Gtk-WARNING **: Allocating size to GcalEventWidget 0x41387a0 without calling gtk_widget_get_preferred_width/height(). How does the code know the size to allocate?