Just come across this bus in Ubuntu Studio 18.04, seems there is no way to report the bug to the Xubuntu team on Launchpad directly. Thunar version in question is 1.6.15 according to the Help page. Bug is pretty simple to recreate: Open Thunar Make sure Tree sidepane is selected. Expand Home in Tree so you can see the folder list. Press Ctrl+H to show and hide the hidden folders. Open a second instance of Thunar and expand the Home folder in Tree as above. Press Ctrl+H - It will show/hide the hidden folders from the Tree in both (all) open Thunar windows! Go back to the original window. Press Ctrl+H - It will only change visibility of the hidden folders in the main pane, not the tree pane. Obviously Ctrl+H should only affect the window which had focus when it was pressed. And it should always affect all parts of that window. Currently Ctrl+H always affects the main section of the current window but the Tree pane is affected globally by the last opened Thunar window.
OK I found the Ubuntu LP page afterwards, as their reporting guide for XFCE components gives broken instructions. Duplicated there at: https://bugs.launchpad.net/ubuntu/+source/thunar/+bug/1774196
confirmed, can reproduce the bug on master
Just realized that Bug #14714 is a duplicate ;) I added a patch there, so I will close this one. I would be happy if you could take a try for the patch, to see if it has any negative side-effects ! *** This bug has been marked as a duplicate of bug 14714 ***