When you start a search [Ctrl+F] in UE, if you have a selected text then it defaults to searching for that selected text in the entire file. This is fair enough.
If you start a Find/Replace [Ctrl+R] it defaults to finding the selected text in the selected text... This one's a bit suspect.
My real point is that in new User Interface design, the trend is to synchronize what's going on in the main window and the search window more intuitively...
For example, [Ctrl+F] also had a ( ) Selected Text then if I change the text in the Find What box, then the scope would change to (*) Selected Text from ( ) Current File. If I switched back to the main window and removed the selection, the Find scope would change to (*) Current File - since there's no longer any selected text.
This would work exactly the same way with Replace. Microsoft VS works in a similar way...
If this gets support I'll submit to IDM (as I did with the RegEx suggestion)