If you pull a blind cord to the right it stays up, if you pull it to the left it comes down. My whole life I've just been jiggling and tugging the cord to get it to stay or come down.
Incidentally, one of the cords on the blinds in my office is worn, and it dis a poor job of engaging. So one side will latch the others will not.
If OP came out assuming a Nairobi design that wasn't used anywhere else, or if they went to the heise.de forums and posted the above; now that would be odd/call-out worthy.
If an American that spoke German did the same in a German-majority space they would be met with pretty massive derision.