[somewhat offtopic] quesion on shell output redirection

I hope there's someone on this list who can easily answer this question off the top of their head. I'm thinking about re-writing the parsing in pcl-cvs to parse stdout and stderr simultaneously, rather than separately. I think this would make it much more robust. Anyway the question is, if I redirect stdout and stderr as follows (in /bin/sh): % some_command > output.txt 2>&1 am I guaranteed that output to stdout and stderr by the program is synchronized? Do the two output streams share the same buffer? I think so, but would like to be certain before undertaking a change to pcl-cvs. thanks greg