Not sure what I did to have this happen so I can't help much with trying to replicate it, (if I figure it out later I'll update this) but the paths in the tabs aren't always showing the correct path. I created a screencast showing the behavior as it happened. In it the tab on the right is showing the correct path while the one on the left is showing the same path as the tab on the right, even though the left tab isn't actually AT that path.
The tab on the left has probably had that path applied to it as a label.
This used to be easy to do by accident if you clicked the tab to start editing the label, then pushed return to accept the label it already had. It'd then stay as whatever it was at the time. Newer versions of Opus ignore setting a label if it's the same as the current label, but it may have been set and saved into a layout or folder tab group in a previous version. (And you could still do it in current versions via more roundabout ways, of course.)
So try clicking the tab to edit its label, then delete the string and push return. That will reset it.