Characters in URL's are getting replaced by HTML entities

campaignmonitor_admin_settings_list_edit_validate() calls check_plain() on the UnsubscribePage and ConfirmationSuccessPage URL's. This causes characters being replaced by HTML entities, ie. & becomes &. After saving a list's settings a few times through the Drupal UI, a URL may become ie. http://domain.tld/node/123?test&456.

A solution might be to check the URL's on form validation and not call check_plain() on these URL's.

BTW: campaignmonitor_admin_settings_list_create_form_validate() does not call check_plain() on any option at all.