Scanner disappointing service unfortunately!

Setting up the printer was easy on the hand and I was very pleased. Since I had to scan large volumes of documents, I set to work at once. The scan quality was flawless as I had only text with 300dpi scan in simplex scanning mode.
But as soon as I switched to duplex scan mode I was surprised about the lousy quality of the scans (blurred). I've tried all the settings, directly depositing both via TWAIN via USB from the Mac or from the Lexmark scan on the Mac. Whether via WLAN or USB connection, the result was always the same, the Duplex Scan both sides will be scanned in an unacceptable quality. One-sided scanning, the quality is again top.

After much back and forth with the Lexmark Service me finally a replacement unit has been sent. But here I have the same problems when scanning. Will now be added even a miserable print quality, which I had not before. This is evident in the air in the pressure lines and comes mM to believe that the "old" cartridges of the first device to be changed in the replacement device. Lexmark sends only the pure printer / scanner without accessories as replacement. The hotline of Lexmark now advised me a "Re-Prime Print Head" to perform, but even that failed and there is still air in the lines!

Now I have 2 multifunction devices, which is neither good nor good scan printing.

Too bad! At first I was very satisfied with the device, to the problems encountered. Therefore, I can not give any recommendation from my experiences! I'm going to try to give back the equipment.

UPDATE 19/12/2012:
Lexmark has now confirmed that it is a Mac driver problem. The scan error occurs only connected to a Mac. If one scans for example to a connected USB flash drive, the result is good.
This is for me the Lexmark device but not as advertised fully Mac compatible and capable and thus my rating unchanged. Too bad that it still has problems with the compatibility of hardware and software with a Mac.