Guys, thanks very much for the answers.
As far as Qn 1 goes, i know I've solved it before, but don't have access to the code (it's in another ctry+company).
As for Qn 2, very informative answer. I kind of imagine these record structs as a tree with the top level hash at the top, so if I accessed anything lower, given you have to traverse the 'tree' from the top down to find it, I assumed it would be shared anyway if you share the root of the 'tree'.
I agree the implementation of shared could (should) be better, thus avoiding the trick you showed me. It's not very elegant ;-) , but that's not your fault of course.
Thx again.
Chris