about 4)

This is expected. Addresses you create by yourself are not considered as change addresses by the
wallet. So they will not appear as child. This may not be what you expect in this case, but this problem
is rather related to the way the wallet recognizes change in general, than to coin control.

make tickets on github.com/Bitcoin/bitcoin if you want attention on these.  The devs don't scour the boards looking for random problems. ( or at least they shouldn't be )

https://github.com/bitcoin/bitcoin/issues?state=open