one of our team is using following structure for working (not totally accurate, but only for example)

• summary issue / target version : work package I
  ** sub task 1 / target version : sub workpackage A
  ** sub task 2 / target version : sub workpackage A
  ** sub task 3 / target version : sub workpackage B

• summary issue / target version : work package II
  ** sub task 4 / target version : sub workpackage A
  ** sub task 5 / target version : sub workpackage B
  ** sub task 6 / target version : sub workpackage B

each subtasks has estimated & spent time on it which are correctly showing up when displaying the summary issue.

however when displaying version work package I & II, it's only showing 0 hours (estimated & spent), assuming it's only consolidating the "first level" and not subtasks.