SDK7: Removing a temporary message display can cause another ui element to move

Background is provided in a comment

Steps to reproduce:

1. Clone the demo scene at Cloning the scene in https://gitlab.com/dcl-tech/demo-uis
2. Be sure that the useGeneralizedCompositing variable near the top of DemoUs.tsx is set to true
3. Run it in preview
4. If you don’t see the 2D Uis appear automatically, click on the green box to open them
5. . // You may have to click a second time, see issue #936
6. Click the button on Ui_2 to maximize Ui_2 and see a second button.
7. Click that second button
8. Immediately, before the Announcement goes away, click the first/original/right button
9. // Expected: the UI will minimize in place
10. // Actual: it minimizes, but jumps to the top left corner of the Announcement panel, and might disappear at the end of the announcement, or remain there for the rest of the scene session

This is really ugly, please fix asap.