diff --git a/js.module b/js.module
index d6bd9f5..c3ee318 100644
--- a/js.module
+++ b/js.module
@@ -88,11 +88,28 @@ function js_preprocess_html() {
 
 /**
  * Implements hook_custom_theme().
- *
- * Used to set the theme to be used for JS requests.
  */
 function js_custom_theme() {
   global $_js;
+
+  // During a full bootstrap, hook_custom_theme() is invoked just before
+  // hook_init(). Here we can make sure that hook_init() implementations
+  // provided by callback dependencies are not invoked twice, in case a full
+  // bootstrap is performed after invoking them in js_callback_bootstrap().
+  if (!empty($_js['module']) && !empty($_js['callback'])) {
+    $info = js_get_callback($_js['module'], $_js['callback']);
+    if (!$info['skip init'] && $info['dependencies']) {
+      $implementations = &drupal_static('module_implements');
+      // After a global cache clear, hook implementation info is not available
+      // yet, so we explicitly rebuild it.
+      if (!isset($implementations['init'])) {
+        module_implements('init');
+      }
+      $implementations['init'] = array_diff_key($implementations['init'], array_flip($info['dependencies']));
+    }
+  }
+
+  // Set the theme to be used for JS requests.
   if (!empty($_js['theme'])) {
     return $_js['theme'];
   }
@@ -669,6 +686,12 @@ function js_deliver($result, array $info = NULL) {
     module_load_include('inc', 'js', 'includes/json');
   }
 
+  // Since most callbacks act at a bootstrap level lower than full, that is
+  // without loading all modules, we need to make sure hook implementation cache
+  // is never written while processing a JS request.
+  $implementations = &drupal_static('module_implements');
+  unset($implementations['#write_cache']);
+
   // Deliver the results. The delivery callback is responsible for setting the
   // appropriate headers, handling the result returned from the callback and
   // exiting the script properly.