Odd behavior with Adobe ClearScan OCRed PDFs

[johnnyb]

I've been using Koreader for quite some time now to make not so very portable documents more so and it all went great until, and it is very odd, since a week ago or so newly created Adobe ClearScan OCRed PDFs started showing a grey background that transferred over to reflowed text (as a sort of halo surrounding the letters and words).
I have not performed any update to my Acrobat reader (it is still version 10.1.6).
I have not updated Koreader prior to noticing this behavior.
I have later updated Koreader to the latest highly and the behavior persists.
The behavior does not extend to older files, only those created less than two weeks ago (from different sources including photos turned into b/w PDFs then OCR'ed and PDFs created from two different scanners).
No “print to PDF” type PDFs are affected (including those where documents are created directly from the source).
And the oddest thing is: The behavior only occurs on my Kindle Paperwhite 3 version of Koreader, my up to date Aura H2O is completely unaffected. The same docs also show up absolutely fine in the built in PDF reader on Kindle.
Has anyone any idea what this might be? I've attached one of the documents and hope that anyone discovers anything that might help me sort this out.