There is a problem with the Arduino IDE on Mac OS X (it seems to also happen on Processing, so maybe they should know, too) that if you type a line of code larger than the width of the window (a single line comment, maybe) a horizontal scroll bar will appear, as one would expect. But if you scroll to the right to view the end of the line and then scroll back to the right, the small default margin is gone, with the code pushed right up against the edge of the window.
I have attached a normal window and the buggy window.
baum
