Okay, I just found out, that the preview of the editor seems to be “faulty”. Even if the entity is set to quote (even a concrete one), the code/preview does not recognize the data as quote.
Another information: It seems only not to be working in the React-app. The desktop-app shows the quote (phew!!!), but when I try to use it within the React-web-app the preview won’t show anything. Strange!
I guess it’s time for a bug-report.