diff --git a/core/modules/system/system.admin.inc b/core/modules/system/system.admin.inc
index f64447e..c2b9312 100644
--- a/core/modules/system/system.admin.inc
+++ b/core/modules/system/system.admin.inc
@@ -680,10 +680,14 @@ function _system_theme_settings_validate_path($path) {
 function system_theme_settings_submit($form, &$form_state) {
   // Exclude unnecessary elements before saving.
   form_state_values_clean($form_state);
-  $key = $form_state['values']['var'];
-  unset($form_state['values']['var']);
 
+  // Extract the name of the theme being configured from the submitted form
+  // values and remove it from a copy of the values, in order to not save it
+  // with the configuration values, but retain it for other possibly running
+  // form submission handlers after this one.
+  $key = $form_state['values']['var'];
   $values = $form_state['values'];
+  unset($values['var']);
 
   // If the user uploaded a new logo or favicon, save it to a permanent location
   // and use it in place of the default theme-provided file.