Strange extrusion width....

Look at the picture. I have set all my extrusion width manually, to 0.6 and 0.68. I was printing this model, and it failed 5 times, always at the same height. So I stayed looking the print, and I noticed that when the model reached somewhere arounf 5mm tall, there were a small area being printed with a crazy amiunt of extrusion, and of course this made a "mountain" of melted plastic wich a layer later made the noozle crash against this mountain of plastic and and that was the cause of the final ruin!
So looking at the sliced file I can see that there are little lines of filament next and around other lines. These little lines are represented in the simulation as haveing ver little amount of extrusion, but actually while they are being print, teh extrusion used is 0.68 instead of what it should be acording to the picture. For some reason slic3r is ignoring my manual width setup. I post a picture for you to see.
Can someone enlighten me why is this happening?

Picture too tiny.

I have caught slic3r trying to extrude lines that were narrower than the nozzle on a few occasions when I allowed slic3r to select the line widths. I have since taken to manually setting line widths and haven't seen the problem again, though some recent support material lines looked suspiciously thin to me.

When slic3r does weird stuff in spite of my attempts at manual control I slice with Cura. Cura seems to do a better job with support material most of the time.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]