I don't know whether it's intended behaviour, but I find it counter-intuitive: When the file browser has the focus, starting a Find (Cmd-F) with search scope 'Document' or 'Selection' does not initiate a search (or give a warning). The expected behaviour is to search in the currently open file (or, if one wants to be fancy, search in the files selected in file browser).
And another anomaly I have just spotted testing this: Having one file open and some text selected and the focus on the editor, opening the Find window with Cmd-F , the Find window opens as expected with 'Selection' as scope. However, actually performing the search finds the needle in a different file within the same project; it'll even open it if it's closed. Strange.
Jonas