computer system have to be use it very careful? or it should be have the user to prevent mistake? http://www.thestandard.com.hk/stdn/std/Metro/GH13Ak01.html

hard to reproduce bug - http://www.drdobbs.com/cpp/its-a-heisenbug/240146005?cid=DDJ_nl_cpp_2013-01-31_h&elq=2a3777bae66d4ddfb7650a070c8ca30b