When I create a folder in the Bookmarks Toolbar and add bookmarks to it, the first shows up like I would expect, but any additional bookmarks do not appear in the menu opened by clicking on the toolbar button for the folder.

They do appear in the "Library" window (accessed using the "Bookmarks > Organize Bookmarks" menu item), and do appear in the menu after a browser restart. So why in the world don't they show up in the folder's menu under the toolbar immediately?