Modal window draggingCurtain lingers when closed while dragging

[vaadin-bot]

Originally by sebgymn

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A modal window places a div with class v-window-draggingCurtain that effectively disallows user to click the background. However, in certain cases, after the window is closed, this element does not go away, rendering the whole application unusable.

STR:

1. Bind escape button (I have not tried other buttons) for closing the window: window.addCloseShortcut(ShortcutAction.KeyCode.ESCAPE)
2. On the screen, while dragging the window from its title (while the mouse button is still down), hit escape button to close the window.
3. The draggingCurtain does not go away and you cannot interact with the application (until you delete that element from the browser inspector).

This can also be observed in https://demo.vaadin.com/valo-theme/#!common
Open a closable modal window and apply step 2.

Thank you.

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Imported from https://dev.vaadin.com/ issue #19574

[TatuLund]

Yes, the issue can be easily replicated with the valo demo application.