I have tripped up over another issue with the new panel flyout menu in InDesign. If you create one or more submenus or separators in your flyout menu, then (for whatever reason) remove them, then reload your plugin, the (removed) items still appear in the flyout menu. They are sticky. They are not properly removed with the plugin. InDesign seems to think they are still there. The only way I have found to remove them is to reset InDesign’s preferences.
The real-world scenario where I think this would be problematic is if you were to release a plugin with certain submenus or separators in the flyout menu, then, at later date, release an updated version of your plugin with changed submenus or separators, you’d have to tell the end-user that, to use your plugin as intended, they had to reset their InDesign preferences. Not good.
Philip