Not sure if encountered a bug or what's going on.
My setup is a Folder Tree pane with Quick Access and This PC. Screen when it works OK:
Preferences > Content:
Preferences > Options:
The problem is, when some folders are navigated to in the lister, tree root changes from This PC to Desktop.
Following screen is after clicking This PC, navigating to it from Quick Access list, again, nothing has changed from above preferences/setup:
Entering e.g. Desktop (also from Quick Access) changes it back to correct This PC root folder:
Same bug happens when navigating to AppData (which I have added as a library folder pointing @ C:\Users\USERNAME\AppData).
I can record a video if requested, but it's pretty simple: sometimes when navigating to folders from Quick Access menu (so far This PC and AppData), screws up my folder tree setup.
Same thing happens if I add identical locations as Favourites, and use it instead of Quick Access list.
Is there any reason this happens?
If you set the tree to start at This PC, and then go to a folder which is not under This PC, the tree will temporarily change to start at Desktop. Otherwise, the tree would not be able to show your current location.
To avoid confusion, leave the "start folder tree at" setting on the default, i.e. Desktop.
Kind weird that it changes the root item though, since "Desktop" (that it changes my root item to) can be found under This PC, so it could just as well expand from under it instead of overriding my settings.
But thanks to your tip I've been able to fix this by just deleting the "special" folders from Quick Access and re-adding them by finding their real directories, right clicking and choosing Pin to Quick Access. Now it works okay (sans special icons for them, but I can live with that).
Desktop is not under This PC.
The folder containing your desktop files is under This PC, but not Desktop itself. (Although Microsoft are making this harder and harder to understand, as File Explorer now shows your desktop folder, not the actual Desktop folder.)
Easy way to tell the difference: Recycle Bin and most of the other things configured under Preferences / Folders / Virtual Folders only appear in the Desktop folder, not in your user-profile desktop folder.