A nag, I know....
I just realised what I did before that made my if.. if.. nesting problem that I mentioned before.
If you have the 'watch variable' window open, or some other function, and you try to re-size the window, and you miss-grab the bottom of the window, you end up dragging a program line to another position. So pleeez, can I have a button somewhere, maybe at the right of the program window, above the arrows, that disables/enables use of the mouse to drag program lines around. These days I only use the arrows to move lines as it's much more controllable.