--- a/web/propertysheet.py	Tue Sep 15 18:43:19 2015 +0200
+++ b/web/propertysheet.py	Mon Oct 05 17:10:36 2015 +0200
@@ -69,7 +69,7 @@
         self._ordered_propfiles.append(fpath)
 
     def need_reload(self):
-        for rid, (adirectory, rdirectory, mtime) in self._cache.items():
+        for rid, (adirectory, rdirectory, mtime) in list(self._cache.items()):
             if os.stat(osp.join(rdirectory, rid)).st_mtime > mtime:
                 del self._cache[rid]
         for fpath, mtime in self._propfile_mtime.items():