Has a bug in oracle bpel, it is fixed duration by expression

          our project has a demand,staffer promises proposer that task would be dealed in ten days ,this  is a duration in bpel task. but  in these days, mybe have weekend days, that is not work days .we must caculate how many weekend days in duration days ,then add those days to duration days.

          I implemented IXPathFunction  interface, test it ,it is working. but put this xpath function into fixed duration by expression place .it does not working . after communicated with oracle staffer.the answer is that it is a bug!

          hope, be resolved ASAP!