I usualy have Folder tree locked, so it's not in sync with my browsing in file displays. I like it better that way.
Now I've tried to turn off Show Folder Tree header and after that it unlocks. When I turn it back on, it's locked again.
I'm thinking it's some kind of bug.
Also, are you maybe planning to add similar customizable toolbar to Folder tree, like File displays now have?
I could use it to put some buttons in there. Now the header only uses space.