Index: fb_canvas.module
===================================================================
--- fb_canvas.module	(revision 4496)
+++ fb_canvas.module	(working copy)
@@ -187,6 +187,10 @@
 }

 function fb_canvas_redirect($url) {
+  // Unset drupal's header
+  if (function_exists('header_remove')) { // php 5.3
+    header_remove('Location');
+  }
   echo "<script type=\"text/javascript\">\ntop.location.href = \"$url\";\n</script>";
   exit;
 }