I have this strange bug happening in Illustrator CS3. If I'm working with a larger file and use the shape tool, Illustrator starts repeating the shape as I scale it. In order to get rid of it, I have to restart my laptop (Mapbook Pro). Since it only happens with larger files, I'm assuming it's a memory issue. I just wanted to see if anyone else had this problem and if you found a better solution. I'm attaching an example of what I'm talking about.
This might be an electromechanical problem with your keyboard, if you have any other working keyboard it might prove this theory to be correct.
The reason I say so is that if you draw a shape with a shape tool and hold the tilde key down at the same time this is exactly what will happen.
Of course if you accidentally hold the tilde key down instead of the shift key when trying to restrain the proportion the same thing will of course occur.
And if you hold the shift and tilde you get a constrained repetitive pattern.