I'm not sure if this will reproduce the bug or not, but I had an existing world open, noticed that the font was FixedSys, and wanted to change it to Lucida Console, 10pt.
The default input and output fonts were already Lucida Console, 10pt, so it seemed that the only way available to change the font in this particular world was to uncheck the World Properties/Appearance/Output/Font/Override with default box, and select Lucida Console with the 'Font' button.
At this point, MUSHClient GP Faults with 'cannot read from location 0x00080010'. I'm working from memory on what the number was.
The default input and output fonts were already Lucida Console, 10pt, so it seemed that the only way available to change the font in this particular world was to uncheck the World Properties/Appearance/Output/Font/Override with default box, and select Lucida Console with the 'Font' button.
At this point, MUSHClient GP Faults with 'cannot read from location 0x00080010'. I'm working from memory on what the number was.