When adding a new page and having multiple layouts for that page (1column, 2column, etc.) the default value of the layout field is empty.
It is possible to save the page with this empty value. But when calling the generated page in the browser an 500 error is shown because of a missing value of the layout for the page.
Sugguestion: The field should have a default value with the first entry of the possible values. Even if this is not the page layout the user wanted initially, at least he's not getting an error.
Annotation: Set to high, because this already led to several customer calls and took a lot of time for finding and correcting the issue.