Notice: Undefined index: skip_alter in core_library_admin_libraries_submit() (line 199 of core_library_ui.admin.inc)

From peterx:

On the settings Library page, what is the difference between all, page, default?
If I hit save on the libraries page, I get lots of:
Notice: Undefined index: skip_alter in core_library_admin_libraries_submit() (line 199 of /var/www/example.com/public_html/sites/all/modules/core_library/modules/core_library_ui/core_library_ui.admin.inc).