Under Wayland the menu of a GtkComboBox with large amount of entries with a high index selected will not appear
glade-previewer -f sortdialog.ui click on the language combobox in the bottom left corner. The button depresses, but no menu appears. There are ~380 entries and entry 61 is set to active.
glade-previewer -f sortdialog-earlier-selection.ui Same dialog, but entry 31 is selected and the menu appears.
Both are fine for me with GDK_BACKEND=x11