I've only noticed it today and I've been using DOpus9 for a while now and very happy with it.
Problem I'm having is that when I open a folder in a new tab and try and move files in to another folder I can't seem to because it has a no entrny symbol on it. I can only move files or folders via the folder-tree and not within tabs.
No, the option doesn't let you do that. The file display in Opus is always sorted/arranged and the only thing you can change is which information the files are sorted by. There's no way to randomly rearrange the files like you can with Explorer in some modes.