This is a KNOWN FEATURE... READ THE MANUAL...
If you read the documentation from XEROX... it claims that on scanning it is a known problem that "Image quality is
acceptable but some quality degradation and character substitution errors may occur with some
originals." page 107 from http://www.cs.unc.edu/cms/help/help-articles/files/xerox-copier-user-guide.pdf
also on page 129 we have the following: "Quality / File Size
The Quality / File Size settings allow you to choose
between scan image quality and file size. These settings
allow you to deliver the highest quality or make smaller
files. A small file size delivers slightly reduced image quality
but is better when sharing the file over a network. A larger
file size delivers improved image quality but requires more
time when transmitting over the network. The options are:
Normal/Small produces small files by using advanced
compression techniques. Image quality is acceptable but some quality degradation and character
substitution errors may occur with some originals."
Of course, for NORMAL it will do substitution.. but what the hell...... It is in the manual.... you do read the manuals, no?