@subSTRATA

about 3)

I can confirm this on windows.
It should not affect coin control functionality, but the checkbox state is misleading currently.
My first thought is that this is related to going from qt4 to qt5, in any case I will look into this.
Edit: Just compiled under linux, yes this is a qt5 bug. I will try to submit this upstream somehow.

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.

Edit: By the way if you prefer the old receive tab, its still available through menu->File->Receiving addresses