
To erase the background of the old line, I originally erased the background of all lines in the visible portion of the source. If the user clicks on a different line, this background must be erased, and then a background must be added under the new line. "Highlight Current Line" draws a light blue background under the line containing the insertion cursor. I then replaced my fix of both "Highlight Current Line" and "Use Block Cursor" with a better fix and the problem went away.
TEXSHOP INSTANT PREVIEW UPDATE
That test gave me confidence to proceed! - Version 5.02 was a minor update which fixed a bug in "Highlight Current Line." I asked Todoroff to turn off "Highlight Current Line" in version 5.08 and the bug disappeared. Program A was 5.02 and program B was 5.01. He reported that A didn't work, but B worked fine. For the next several days, Todoroff tested versions of the program which I sent him. Although he was using version 5.08, he told me that versions 5.00 and 5.01 typeset without problems but version 5.02 often failed. Luckily, Todoroff knew exactly when this bug was introduced. Just before typesettting concluded, his console would stop reporting output and the program would become unresponsive.

Kurt Richard Todoroff reported an important bug that I could never reproduce. Just check the box "Use Also for Macro Editor" under the Console Tab. To avoid cluttering the Preference Dialog, version 5.09 allows users to also use this console font in the Macro Editor. There is already a preference to change the default font in the console.

TeXShop 5.09 - Marco Santi wanted a preference to set the font and size of text in the Macro Editor.
