This might be true for other platforms too, but I’ve only noticed it on Cocoa.
I have a Templates menu that starts with two items, “Open Templates Folder” and a separator. In code, the contents of a folder is added or updated when EnableMenuItems is called, and that works fine. But if I launch my app and immediately pull down that menu, the separator doesn’t appear. If I release and pull it down again, it shows up. Or if I start up and immediately pull down any other menu, then move to Templates, it looks fine. If I call EnableMenuItems during startup, it’s fine too.
I’ll try to create a project that shows the bug.