Error after creating a new blank page

Steps to reproduce:

• Go to a space and create a new blank page
• The editor will be opened and now enter title and content
• Click again on the Create button in the main menu (the editor is still open)
• A browser popup appears asking if you really want to leave the page - confirm it
• A new editor will be open
• Confirm that you want resume editing the page
• If now you click on Close the editor you will be redirected to the editor before (just like a browser back) which works but clicking again on the close button it ends up with a "Oops - an error has occurred".

Stack Trace:[hide]
java.lang.IllegalArgumentException: Space key is required
	at org.springframework.util.Assert.isTrue(Assert.java:65)
	at com.atlassian.confluence.pages.DefaultDraftManager.create(DefaultDraftManager.java:245)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)

I noticed the behavior on Confluence 5.7-beta8, 5.7-beta16 and 5.7 (release from yesterday).
On a previous version(5.6, 5.5, ...) the close directly redirects to the starting page before Create was clicked the first time.

From my prospective, it would make sense to disable Create if the editor is open and the user must decide to close or save the page if s/he wants to create a further new one.

Best regards
Sven