Here's a possible improvement:
Current situation: Open any file in Arduino IDE 1.0 that provides more lines of code than what fits in one screen heigth. Now try to select the bottom 5 lines of code.
What I'd expect to happen: Scrolling starts only if selected area (actually mouse pointer) moves below horizontal scrollbar (as a reference, try out notepad++ and see what happens there)
Additional facts: I just realised the same (even if not that bad) happens horizontally.
Note: This is no backbiting. Arduino rocks. Period