The values for "Show all whitespace for:" field gets blanked out upon saving even though they are stored in the database. 

The reason is that SiteSettingsForm.load is called *after* the initial value for include_space_patterns is setup. The values that are setup by DiffSettingsForm are overwritten by SiteSettingsForm thus blanking out the value. Calling the super.load before setting up the initial value for include_space_patterns solves this problem.

manual testing