* Known problems

 + When all the following requirements are met, the file is not sent.
   It is a feature.

   1. The clock of a remote machine is pretty faster than the local's one.
   2. The cache file is broken or nonexistent.
   3. The timestamp of newly updated file is older than the timestamp of
      the same file before updated on remote side.

   The problem is not caused as long as the timestamp cache facility
   works correctly.
   The most easy and absolute way to avoid this problem is asking the
   administrator of a remote server to put the clock right. :-)