One doc-Tabs-Conntent view, expand "Additional tab configuration" and annoying dialog

Studio. Click the def. of a document.
Go to the "Tabs" tab.
Go to the "Content view" sub tab
Expand "Additional tab configuration"
Do nothing else (you expanded it just to check what's inside)
Click another tab. ANyone. "creation layout" for example.
=> A browser alert, "Validation Error: Content view selection is required"
No way to quit this form without discarding or saving.