I was trying to implement a multiple-level TabMenu. Since it's not currently supported, I tried a workaround: placing a popup menu and call the show (or toggle) method with the event provided by the onTabChange event. My surprise being it crashes because of the offsets not being available. Then I tried to get the native event and pass it to the menu, but then it's display at top:0, right:0.
I've been throwing a handful of hours trying to debug this issue, and it seems to be related to the synthetic event trigger by the TabMenu not referencing the target properly (at least, when the Menu tries to get the rect and the offsets, the target property it tries to access is null). I couldn't dive deeper so I desisted and used MenuBar.
Is this behaviour intended?