1. Have a couple of As and select some:
2. Press Ctrl+F.
   You'll see a line around your selection:
   
3. Press A.
   All the As found in your selection will be highlighted:
   
4. In the "Replace with" edit, type B and click "Replace All".
   All the found As will be replaced correctly but the selection changes:
   

The selection should still be the same as before replacing. In this example, all inserted Bs should be inside the line.