About "Launching DO will launch FTP" and getting Opus to NOT start with the problem folder... Maybe you have the "update default lister automatically when closing a lister" option enabled? And each time you encounter the problem after double-clicking a sub-folder from Win Explorer launches Opus, then have to kill Opus - the default lister starting folder is being reset to this ~problematic NAS folder? If so - you may want to disable that option until this gets sorted out, as well as obviously making sure none of your layouts (default, user specified layouts, etc) are actually set to point to that location as the starting folder?
Besides that, the screenshots and the login prompts bother me as well... and what Leo noted about that entry being located under the "Computer" node in the folder tree definitely seems to scream out that the initial treatment of that folder might involve something not "standard", or otherwise at least not "expected by Opus".
Based on mrwul saying that disabling explorer replacement eliminates the problem with double-clicking from Win Explorer... it certainly sounds like Opus is being asked to treat it like a 'regular folder' based on normal Explorer Replacement rules (rather than explicitly as an FTP site). Whether by shell extension or some other means, I'll bet that the appearance of this path under the "Computer" node in the tree has more than just a cosmetic effect on how Opus is working with it... BOTH in terms of how it's failing to list the folder properly and becoming unstable, but ALSO in how you've been unable to "exclude" Opus from handling this path - which I think is still a good idea, but probably not working because the path being passed to Opus is different than the "ftp://" path you added to Prefs; making Opus unable to match it with anything in your exclusion list in order to say "I don't want to open this myself so I'll ask Explorer to open it after all" (paraphrased from Leo's explanation on how folder requestes are treated in Explorer Replacement mode).
...More curiosity than anything else, but - if you actually add this IP address and folder as an 'actual' ftp site in Opus FTP address book... does it work fine in Opus then? Apologies if I missed any comments on that already in the thread.