Tooltips can be displayed behind some Editor sub-windows on Mac

Using Command-Tab on a Mac to go to another app and then return to the Editor will result in some tooltips being displayed behind Editor sub-windows.

1. Open a project in the Editor.
2. Hover over a button in the toolbar that so that a tooltip is shown.
3. While the tooltip is visible, press Command-Tab to go to another app.
4. Press Command-Tab again to return to the Editor.
5. Select Add New -> Blueprint Class.
6. Hover the mouse over one of the Common Classes buttons.

RESULT:
The tooltip appears behind the Pick Parent Class window, making it unreadable.

EXPECTED:
The tooltip appears in front of the window so that it can be read.