diff --git a/composer/composer/InstalledVersions.php b/composer/composer/InstalledVersions.php
index 07b32ed6ef..6d29bff66a 100644
--- a/composer/composer/InstalledVersions.php
+++ b/composer/composer/InstalledVersions.php
@@ -32,6 +32,11 @@ class InstalledVersions
      */
     private static $installed;
 
+    /**
+     * @var bool
+     */
+    private static $installedIsLocalDir;
+
     /**
      * @var bool|null
      */
@@ -309,6 +314,12 @@ public static function reload($data)
     {
         self::$installed = $data;
         self::$installedByVendor = array();
+
+        // when using reload, we disable the duplicate protection to ensure that self::$installed data is
+        // always returned, but we cannot know whether it comes from the installed.php in __DIR__ or not,
+        // so we have to assume it does not, and that may result in duplicate data being returned when listing
+        // all installed packages for example
+        self::$installedIsLocalDir = false;
     }
 
     /**
@@ -325,7 +336,9 @@ private static function getInstalled()
         $copiedLocalDir = false;
 
         if (self::$canGetVendors) {
+            $selfDir = strtr(__DIR__, '\\', '/');
             foreach (ClassLoader::getRegisteredLoaders() as $vendorDir => $loader) {
+                $vendorDir = strtr($vendorDir, '\\', '/');
                 if (isset(self::$installedByVendor[$vendorDir])) {
                     $installed[] = self::$installedByVendor[$vendorDir];
                 } elseif (is_file($vendorDir.'/composer/installed.php')) {
@@ -333,11 +346,14 @@ private static function getInstalled()
                     $required = require $vendorDir.'/composer/installed.php';
                     self::$installedByVendor[$vendorDir] = $required;
                     $installed[] = $required;
-                    if (strtr($vendorDir.'/composer', '\\', '/') === strtr(__DIR__, '\\', '/')) {
+                    if (self::$installed === null && $vendorDir.'/composer' === $selfDir) {
                         self::$installed = $required;
-                        $copiedLocalDir = true;
+                        self::$installedIsLocalDir = true;
                     }
                 }
+                if (self::$installedIsLocalDir && $vendorDir.'/composer' === $selfDir) {
+                    $copiedLocalDir = true;
+                }
             }
         }