Issue #2947281 by focus13: Single on/off checkbox is always checked

src/Plugin/views/exposed_form/BetterExposedFilters.php

@@ -1110,8 +1110,36 @@ Title Desc|Z -> A</pre> Leave the replacement text blank to remove an option alt
 
           // Use filter label as checkbox label.
           $form[$field_id]['#title'] = $filters[$label]->options['expose']['label'];
-          $form[$field_id]['#return_value'] = 1;
           $form[$field_id]['#type'] = 'checkbox';
+          // Views populates missing values in $form_state['input'] with the
+          // defaults and a checkbox does not appear in $_GET (or $_POST) so it
+          // will appear to be missing when a user submits a form. Because of
+          // this, instead of unchecking the checkbox value will revert to the
+          // default. More, the default value for select values is reused which
+          // results in the checkbox always checked. So we need to add a form
+          // element to see whether the form is submitted or not and then we
+          // need to look at $_GET directly to see whether the checkbox is
+          // there. For security reasons, we must not copy the $_GET value.
+
+          // First, let's figure out a short name for the signal element and
+          // then add it.
+          if (empty($signal)) {
+            for ($signal = 'a'; isset($form[$signal]); $signal++);
+            // This is all the signal element needs.
+            $form[$signal]['#type'] = 'hidden';
+          }
+          $input = $form_state->getUserInput();
+          $value = \Drupal::request()->query->get($field_id);
+          $checked = isset($input[$signal]) ? isset($value) : $form[$field_id]['#default_value'];
+          // For security, we check if value is valid and exist.
+          if ($checked) {
+            if (!in_array($value, array_keys($form[$field_id]['#options']))) {
+              $checked = FALSE;
+            }
+          }
+          // Now we know whether the checkbox is checked or not, set #value
+          // accordingly.
+          $form[$field_id]['#value'] = $checked ? $value : 0;
           break;
 
         case 'bef':