[NTG-context] problems with / bugs in naturals tables?

Hi all! I try to use ConTeXt to set tables specified with the CALS table model. Everything that is needed for this task is provided by the natural tables. Yet, the results are rather unsatisfactory. In particular I encounter the following problems: 1. The table header that is to be repeated after every page break includes a lot of whitespace. This white space is not contained in the provided input. 2. The frames of cells are extended bellow the bottom margin if there is a nr-attribute greater than one and a page break is necessary. In order to illustrate these problems, I attach a ConTeXt file and the produced pdf. Does anyone know about these problems? Is there a workaround? Thanks for your attention, --Stefan