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as Birgit has meant in the comments below, this plastic strip was the problem. then I have about 40-50cm long plastic strip pulled out and it's black again! that it was not a sufficient statement nevertheless is a minus point. now I'm back happy with this replacement toner ;-)
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edit on 12/19/2013: I got myself a second toner. This time, the mentioned plastic strip is completely gone, and the toner is working properly from the beginning. Excellent! :)