Ticket #32783: 32783.diff

src/wp-admin/js/customize-controls.js

@@ -2331 +2331 @@
                                 api.HeaderTool.UploadsList,
                                 api.HeaderTool.DefaultsList
                         ]);
+
+                        // Fix ajax issue in customizer when previwing different theme which supports header image in customizer 
+                        $.ajaxPrefilter(function( options, originalOptions, jqXHR ) {
+                                if ( 'custom-header-crop' === originalOptions.data.action ){
+                                        options.data += '&wp_customize=on&theme=' + api.settings.theme.stylesheet;
+                                }
+                        });
                 },
 
                 /**