I noticed this change too. It has benefits and a drawback, I suppose.
I don't know if you have noticed how the Solo editor button and edit active part button interact, so to speak.
Building on the OP's example: I've opened two parts in Key Edit.
- Solo off, Edit Active Part off: All the parts in the project play; all parts in the editor are editable.
- Solo off, Edit Active Part on: All the parts in the project play; only the active part in the editor is editable
- Solo on, Edit Active Part off: Only the parts in the editor play; all parts in the editor are editable.
- Solo on, Edit Active Part on: Only the active part editor in the editor plays; only the active part in the editor is editable.
To get the Cubase 6 behavior now, you have to Solo all the tracks you want to hear in the project page, then go into key edit, turn off the Solo editor button, and activate Edit Active Part Only.
I find this new behavior better. I agree there should be a pref to get the old behavior. I won't comment on the likelihood of seeing that– I have learned to be flexible, and the new way is now integrated into my 'workflow'.
"We've always been at war with Eastasia"