It's been mentioned before. But the option to Preserve folder tree expansion when switching tabs still seems to be doing the opposite of what it says.
As soon as i turn it on and switch a tab, the folder tree is reset for all tabs, leaving each tab with only their current folder location. In fact it even goes so far to collapse said folder despite having Expand selected branch enabled. (though the additional "..when changing tabs" fixes that)
The only time expanded folders are preserved is when opening a new tab, but just switch to another tab and everything is collapsed again. This is again where one would expect the opposite: For the new tab to start its own journey, and for the existing tab to be preserved exactly as-is.
ps. Collapse non-selected branches is OFF.
You've probably misunderstood what the "Preserve folder tree expansion..." option does. I did the same when I first started trying to confirm this, but the manual explains it properly:
Preserve folder tree expansion when switching tabs : When this option is on, the expansion state of folders in the Folder Tree will be preserved between tabs. That is, when you switch away from a tab, Opus remembers which folders in the folder tree were expanded and which were collapsed, and restores this state when you switch back to that tab.
So it does not keep things expanded when you switch tabs. It remembers which things were expanded separately for each tab, and restores that state when you go back to a tab.
That's the thing though, it doesn't.
Please read what i wrote again, because I don't know how else to say it.
Everything that was expanded is collapsed when switching tabs, as if it is actively doing so. The tab's folder is opened back up, but everything else forgotten.
Even when you switch back to the tab where things were initially expanded?
The Expand selected branch option would do that. Maybe it's also interfering with the Preserve... option, but I'm not sure. I did most of my testing with that turned off to avoid complicating things with another option expanding things as well as the one I was trying to check.