Caught-in-the-middle extrusion

[3poro 9]

I'm running UM2 with Cura 14.03 and the latest firmware, the material in use is PLA Silver-Grey from Ultimaker. My layer height is 0.1mm, print speed 50mm/s and I'm using default PLA settings from UM2. My need is to print a solid (100%) object and I have trouble getting the extrusion right.

The wall (both fully vertical and the one in 45 degree angle) is beautiful; it's smooth and virtually flawless. The screw hole walls are on the brink of getting over-extruded - there are problems if I pump the material flow up from 100%. At the same time, the bottom is seriously under-extruded. I can actually see rays of sun through it, even if the material is 2mm thick.

In Cura, I have set the shell thickness as well as the bottom/top thickness to 1mm - and the fill density is 100%.

Feeding of material seems to work normally. I have had similar problems with ABS, but not quite to the same extent.

Is there some setting which I'm missing? The problem seems to be mostly related to infill, IMHO.