[NTG-context] placefigure & headers topframe interactions

Hi all, I use in my document: \setupbackgrounds[header][text][bottomframe=on] \setupbackgrounds[footer][text][topframe=on] in order to obtain black rules. Since I don't want the topframe on in the chapter's first pages, I use in setuphead the option header=high... It works if I have only text in my document, but when I use \placefigure[here][fig:afigref]{A dummy label}{\externalfigure[dummy]} to include METAFUN or pdf graphics, I obtain a black rule (topframe) on top of the first page of the next chapter... Seems very strange... I tried to solve the problem but, unfortunately, without success ! Any idea ?