Well that shouldn't happen... I'll look into it.
In the mean time, try using BoneFollower (it's independent of Skeleton Utility) instead of Spawn Hierarchy.
Found it. If you don't have any Override bones it never registers to the post-skeletal update event... this was an oversight on my part. Add an Override bone to something and uncheck all of its checkboxes (effectively disabling it) to force SkeletonUtility to update correctly. I'll fix this properly today or tomorrow.
