In VisualEditor:

1. Insert Template with at least one required parameter (per template data).
2. Ensure the value is empty.
3. Attempt to save.

Expected:

"Required parameter missing" dialog is shown. This dialog should not have aria-hidden. The original template dialog should now have aria-hidden.

Actual:

Both now have aria-hidden.

At first there were two empty window managers, neither aria-hidden. Then the template dialog is opened, which marks all other top-level elements (including the second, currently empty, window manager). Then a message dialog is created, which hides all other window managers. But forgets to unhide itself.