https://github.com/mitsuhiko/flask/issues/487
diff -ur Flask-0.10.1.orig/flask/helpers.py Flask-0.10.1/flask/helpers.py
--- flask/helpers.py	2013-06-14 06:35:43.000000000 +0800
+++ flask/helpers.py	2013-08-16 16:18:36.194006290 +0800
@@ -679,7 +679,7 @@
             filename = sys.modules[import_name].__file__
         package_path = os.path.abspath(os.path.dirname(filename))
         # package_path ends with __init__.py for a package
-        if loader.is_package(root_mod_name):
+        if package_path.endswith('__init__.py'):
             package_path = os.path.dirname(package_path)
 
     site_parent, site_folder = os.path.split(package_path)