When data-comparing two databases, one should be able to change the database in "edit comparison" screen without all selections in the "mappings" screen be initialized. In more details: if one has to compare several databases to a master one (which usually have the same or almost the same structure), there could be a checkbox to "keep previous mappings when changing the database". So, if the previously compared tables are also identical in the newly selected databases, the selected tables and selected comparison keys/columns/filters should be preserved.