This is very strange... I thought I was going mad for a while.
Coincidentally, within 5 minutes, I found two things that only work in the first lister I open:
dynamic thumbnail resizing. Since I've only just enabled it, I thought it just didn't work at all at first, until I moved to the first lister I had open, where it works. However, any subsequent lister I open just doesn't do it. Dragging the slider doesn't make the icons change their size!
rename. In the first lister I have open, the rename option brings up the proper dialog box as you'd expect. In any other listers, rename will only do inline rename!
Hm, OK, doesn't seem to be quite that simple. Having closed the first one, any I open seem to be working as you'd expect. So I guess all I can say is that in certain circumstances, it doesn't work... not very helpful, I know!
When things didn't work you were probably looking in folders that Opus displays using Explorer, where functionality will be slightly reduced/different.
That should only happen in "virtual" folders like Computer and Desktop. (Go to /desktopdir instead of Desktop and you can view it as a real folder.)