Reproduce: 1. Open Places Pane 2. Select Devices > Harddrive (the Root one), (can also be reproduced with a connected USB drive) 3. Navigate to /etc/alternatives 4. Open the Folders Pane 5. Notice, that the folder tree is only synced up to /etc. Normally, /etc/alternatives would be selected In this case, I also noticed that the sync'ing does not work when I browse anything that is not part of my /home folder.
Might be same cause as https://phabricator.kde.org/D10016
/etc/alternatives is correctly selected for me with Dolphin 18.12.2. I assume that this bug was fixed with the patch from Kai that he referenced. Please reopen this bug report if the folder isn't correctly selected for you.
Works for me, too, now.