diff -upr sites/all/modules/boost_orig/boost.module sites/all/modules/boost/boost.module
--- sites/all/modules/boost_orig/boost.module	2008-10-25 21:30:34.000000000 +0400
+++ sites/all/modules/boost/boost.module	2009-01-24 18:04:02.000000000 +0300
@@ -548,8 +548,10 @@ function boost_file_path($path) {
     return FALSE;
   }
 
-  // Convert any other undesirable characters in the path to underscores:
-  $path = preg_replace('@[^/a-z0-9_-]@i', '_', $path);
+  //Paths with undesirable characters will not be cached:
+  if (preg_match('@[^/a-z0-9_-]@i', $path)) {
+    return FALSE;
+  }
 
   return implode('/', array(BOOST_FILE_PATH, $path . BOOST_FILE_EXTENSION));
 }