It all depends how they're opening the folder. There's an official API function call that apps can use, and if they do then Opus will intercept it. Unfortunately not a lot of developers know about that function, so they end up doing it one of several other ways, only some of which can be intercepted.
We'll have a look and see but it's possible there's nothing we can do from our end, the developers of the other app would need to make a change to enable this to work properly.