The question whether or not the number mangling in scanned documents only occurs at Xerox devices seems to have been answered. I got an eMail of a Brother customer telling me he's able to replicate the issue using my test number sheets on a Brother MFC-9140CDN. He attached the outcoming scan and indeed, there is at least one 6 substituted by a nice, clean 8.
Edit: Brother replied and stated that their devices are not affected by number mangling. At first glance, the Brother MFC seems to substitute a lot less numbers than the Xerox machines. Of course, as I haven't been able to reproduce the error on the machine myself, and additionally, the device ID is not shown in the PDF (there only is to be read “Paperport 12”), so I can't really tell where and how the data has been processed, so please take the information as hearsay. Also, we can never be sure the mails I get are part of some spin doctoring campaign, so be suspicious. I'll be adding potentially affected devices to my “hear-say list of affected devices” though.
Whats more, until now it looked like the newer Xerox devices (WorkCentre 78xx) would not be affected. Unfortunately, I may have to destroy this illusion as I got an email from someone familiar with the topic, telling me that one of his customers is able to replicate the problem on a bunch of eighteen 78xx machines. However, this is no real confirmation at all as I haven't seen any scans of these. Also, I'm investigating what particular 78xx devices are affected.
Next thing: Xerox seems to be telling their support right now. Thus, by someone saying he is xerox support employee (I can't verify this) I got a list of potentially affected devices as Xerox seems to have investigated theirselves. Let's cite the list:
As well: Take it as hearsay. Imagine that Xerox could have scanned the list on one of their own devices.
Edit: Xerox has been preparing some Q&A sheets, have a look: