3.0: Nested Rich text widgets break after initial creation

## To Reproduce

> 1. Use `theme-build` https://github.com/apostrophecms/a3-demo/tree/theme-build
> 2. Install, login, etc
> 3. On the homepage, add a Two Column widget
> 4. Save the initial modal with two empty areas
> 5. In one of the two new areas, add a Rich Text widget .. add content to this widget (success)
> 6. Refresh the page and re-edit the rich text widget, see it lose focus and call its `UPDATE` event after a keystroke or two

## Expected behavior
> Editing rich text in a nested widget should behave

## Describe the bug
> A clear and concise description of what the bug is.