pressure advance feature not doing anything

Hello,

I wanted to try out the pressure advance feature of Slic3r, but I'm having some problems with it:

I usually have set a 3mm retraction (bowden), and it always worked fine.
When enabling pressure advance, I'm getting extractions of about a full cm?! Even when pressure advance is set to only 1.
This pulls molten plastic into my cold end, which makes me disassemble the whole extruder every time..

However, I just disabled retraction and then this no longer happens.
Apart from that, the real problem is that I can't seem to get the pressure advance working.

In the picture you can see the top part (pressure advance=0) and the bottom part (pressure advance=10)
But both look just the same to me.
I was expecting the thick corners to become thinner, but it does not work.
However, at the start of the print (only when pressure advance is enabled),
the extruder does extrude a lot of material to pressurize the hot end, so it does actually do something.

It is marlin software, and I'm using the Repetier environment.

If anyone could help me out on this, it would be greatly appreciated (;

I have the same issue with pressure advance doing big retracts. I am using firmware retract though, so I'm not sure it's related. There may be some interaction with volumetric extrusion, as I set the filament diameter to the magic 1.2 something in the slicer and the firmware controls computing the extruded volume. However, I think it might not use volume measures for retraction so it might pull inappropriate amounts on retract and unretract, interfering with pressure advance.