I haven't seen something like this before, I guess you can try to run the following command in command prompt and see if it is set to the correct timezone:
\program files\pipc\adm\pidiag -tz
If the command gives you the timezone setting as a timezone of UTC-8, then it is possible that there is a localhost.tz on the client machine that is still providing the old timezone settings. You probably want to search for this file to delete it.
Another possibility is that your client machine has a TZ variable defined in the system's environment variable. This can override the system's timezone setting and cause this problem.