copy/paste is app specific as some apps have written custom code to access the copy/paste functionality. I would guess apple will continue to try and lock this down more in future as they see it as a security issue to protect apps form accessing data when you aren't actively copying/pasting but have something copied.

On most apps you can swipe from the left edge to the right and it will take you back without hitting the back arrow. This is a feature that slightly depends on the app, but could be a workaround for you issue at times of not having a back button. Some Developers have turned this off or use custom coding that doesn't support this.