ok, partialy i have found the issue. in the article by deckingman there is a paragraph that refers to extruder numbering. i suggest to extend it by following
[[language]] slic3r on object -> settings it is offered to choose extruder from the "default" (that is prompted to be 0), "1", "2", "3" and "4". In fact, slic3r treats "default" as "1". Later in generated gcode this "default"="1" is treated as "T0". "2" is treated as "T1" etc.another issue that i look into now - even for very simple things (circle) it generates 5 tool changes, that can be difficult with manual filament change.