Steps to reproduce:
1. Open https://jsbin.com/wihowazami/1/edit?html,js,console,output on Safari Desktop
2. Activate VoiceOver.
3. Focus on the "Menu button" button.
4. Activate the menu button with VO+Space.
5. Try to move to the second menu item with VO+ArrowRight.
6. See the console output that says the first menu item has been clicked.
I just would like to add that this bug happens when the role=menu element is initially hidden (e.g., with display: none), which is the case for most menu widgets.