emacs - Org Mode iCalendar export non-unique UID generation -

i using emacs 23.2 , using org-mode keep track of tasks. have quite list of tasks have made events mentioning time period , adding scheduled tag tasks.

when export task icalendar file, using c-c c-e i command, .ics file many of tasks have same uid though date , time stamp mentioned different. why so? there way can generate unique uids in org-mode?

i tried customizing uid format variable %s%temacs , other list of format specifiers in customization not seem work.

has faced kind of problem?

thanks shyam