I can map like this:

mMapVoucherPos->addMapping(ui->cbCostCenter->lineEdit,8);

and the combobox in the dialog shows the right value, but I cannot submit to the model!

No, the column I am seeing in the combobox is the right column (the column with the text = column-ID 1).

The value that is written into the database is not the value from the linked Key-Field ("AdrKey" = first column of "kontake" or "vkontake" = column-ID 0), but the Index (currentIndex) of the row that is selected in the combobox!!!