When Drupal Timezone is set through DateAPI, events startdate/starttime in CiviEvent are not handled properly by the Views handler for the CiviCRM Views Integration module.
For example. If my Date timezone is -8, any CiviEvent with a start time before 8am will be shown on the previous day of the Calendar. If my timezone is +8, it would be shown on the following day.
My guess is this is something to do with the CiviCRM Views Integration module and how it handles (or does not handle) the starttime as it relates to the Date Timezone set in Drupal's Date API.
Please check to make sure it is working. The maintainer of the Calendar Module has been unresponsive. See post here with 2 reports of a bug: http://drupal.org/node/911934