I get the correct results in Explorer or using the Tools > Find Files dialog instead.
It seems like selecting the folder from the Folder Tree using the same search results in a global search rather than a constrained search using the selected directory. To reproduce it, close all windows. Open a desktop folder (not the desktop itself) and use the search bar to search for a common term that might show up in a subdirectory. In my case I selected "Desk Current" in the folder tree and searched for "ffl". Results here:
Now, from the same window, select another folder in the Directory Tree. In my case I selected "Harbor Freight". The winodw displays all files in the Harbor Freight folder (as expected) Now re-enter the same search term ("ffl") in the toolbar and, as shown by the paths, the results are global:
FWIW, in the search toolbar, the search results returned (constrained or global) seem random regardless of where the search originates. Sometimes I get the correct (constrained) results, sometimes global results. It's just that the above method is reproducible.
I wonder if (one solved) it should be an option to return constrained or global results? I looked in the preferences figuring it was an optional setting.