How to avoid post FileContents when editor is closed?

I have integrated Collabora in our web application. Now I noticed an unexpected behaviour:
When the IFrame with the editor is closed or removed from the visible page part, than the editor sends a Post request with the last file content similar as if the user has triggered the action save.

Is this behaviour expected? How can I avoid the last post request from the editor to my wopi host?

Thanks for hints