Allow modification of existing text selection with shift-click

After a selection is made you cannot modify the selection by shift-clicking. This is either a bug, or maybe there's a preference that I'm not aware of. As I'm sure you already know, pretty much every text editor allows you to modify your selection with a shift-click. By modify, I mean either add text to the selection or remove selected text from the selection. This doesn't work for me on Windows 7 x64 using version 2.0.1.