I have the CS 767-200 and 767-300 and I noticed recently  that on the 767-300 the vertical speed indicator is not working.  I don't often fly the CS's 767-300 and that's why I noticed the problem recently.  I switch each IRS to Align then to Nav, wait about 25 seconds then all instruments display functionality except that the VSI is still off and later on in flight the attitude indicator loses sync with the aircraft's attitude.  I reinstalled the CS 767-300 and it still had that problem.  Did I miss a step in preparing for flight or is this a bug that need's to get fix?