RX100 has massive problems with F1.8 Close-ups

My RX100 has massive problems with F1.8 Close-ups.

The pictures are all blurry and soft, the contours with hard contrast have white or blue flames and the white balance often shifts into the blue.

I've made a few test shots (Warning big file size)

Here you can see the comparison between the RX100 and a Canon S100

In order to confirm my first impressions I have made a shot at F1.8 and F5.6 with a tripod ​​.
The picture at F5.6 is sensationally good, the picture at F1.8 a disaster.

http://mb-g.info/Samples/Crop 1.8_1.jpg
http://mb-g.info/Samples/Crop 1.8_2.jpg
http://mb-g.info/Samples/Crop 5.6_1.jpg
http://mb-g.info/Samples/Crop 5.6_2.jpg

Here an other close-up at F1.8 anf F5. Look at he color and the edges at F1.8

Any idea what the problem is with the camera?