Presetting tools for infill etc... ( multi-extruder )

Since I'm printing with a diamond hotend, I'm using slic3r and managed to make it work ( more or less )
But what puzzles me is the tool to preset, which extruder tool is used for the different parts of a print ( infill, solid infill, skirt/raft etc )
I've set the skirt/raft extruder to tool 3 from the beginning but it never worked.

Now I tried to print the infill with a different extruder and this sometimes work but sometime doesn't.
To my surprise, the skirt prints different too, when the infill tool change is recognized by the slicer.

What am I doing wrong, that it works one day, but not the other?

Edited 2 time(s). Last edit at 12/03/2016 06:47AM by o_lampe.

I think, I figured it out:
You must not assign an extruder in the part-settings, but keep it "default". That's a pity, because now I can't have parts with multiple sections and still print the infill in carbon reinforced filament or the like.
I can either assign a virtual extruder to a section or print it in different material mixes.

Wouldn't it be better to use the assigned virtual extruder for the perimeters only and the rest follows the settings in "multiple extruders"

Edited 1 time(s). Last edit at 12/04/2016 10:13AM by o_lampe.