JBIG2 was never meant for text scanning, only for pictures. It analyzes the scan and replaces information with as much of the same information as possible. That's what lossy compression is.
Say if you have a nice picture with the same 20 brown items on it, it will remove 19 an replace each with a copy of the first one, therefore greatly reducing the file size. Only if you carefully examine the picture you will notice the strange artefacts.
Sadly, it's not for text, since it will sometimes not see the difference between a 6 or a 8 (amongst other things), therefore giving lots of errors.
All it's doing is recognizing "similar" patches of the image and coalescing them, which is what it's supposed to do, according to the standard. Yes, it's too aggressive for text.
Xerox already responded:
The problem stems from a combination of compression level and resolution setting. The devices mentioned are shipped from the factory with a compression level and resolution that produces scanned files which are optimized for viewing or printing while maintaining a reasonable file size. We do not normally see a character substitution issue with the factory default settings however, the defect may be seen at lower quality and resolution settings.
The Xerox design utilizes the recognized industry standard JBIG2 compressor which creates extremely small file sizes with good image quality, but with inherent tradeoffs under low resolution and quality settings.
For data integrity purposes, we recommend the use of the factory defaults with a quality level set to â€œhigher.â€ In cases where lower quality/higher compression is desired for smaller file sizes, we provide the following message to our customers next to the quality settings within the device web user interface: â€œThe normal quality option produces small file sizes by using advanced compression techniques. Image quality is generally acceptable, however, text quality degradation and character substitution errors may occur with some originals.â€