I recently bought mine from Germany. I updated the firmware to 2.1.3 over WiFi and also experienced the fading for normal - not scanned - PDFs. I installed 2.1.2 from pocketbook-int.com, but the same result. Tried the same from the German site and the same result.
I was considering sending the 912 back and ask for a refund. Then I tried the 2.1.2 from the Russian site and the problem with PDFs seems to have vanished!
I haven't tried their 2.1.3, since I have had enough and large technical PDFs is what I bought it for.
If they can offer PDF cropping and font boldening as under Duokan for my Kindle keyboard, this e-reader would really be worth the 230 euros I paid for it.