Hi,
I'll look into why it is behaving this way in more detail with Carlos but it looks as though it is to do with the order of evaluation. If you turn off the mirror node you can see that the handrail's position changes to the higher level you're seeing in the file you sent me.
This also explains why the Padding fixes the issue, because the handrails position then ignores the size of the end cap.
Thanks,
Paul