Couldn't find if this has been reported before, but once a page "Entry Point - Is Default Layout" is selected, it can't be de-selected.

I don't really know what this does.

The entry point in to know what file to call by default.

If your component is called without parameters (index.php?option=com_mycomp)

You cannot deselect, but you can select another, and it will unselect which you want.

Note : A collection layout entry-point, is always called 'default'