Eicon Diva Pro 4BRI8 and PTP problem

I have this strange problem regarding an Asterisk with a Diva Pro 4BRI8 and 4 PTP channels ISDN. When i plug in all the ports of my NT’s, the Diva doesn’t pick up all the lines. It seems i can only call out on 2 channels, and it picks up every 2nd-3rd call or so, the rest of the calls are discarded. This is kind of frustrating…
When i do a capi debug, and i call in, the calls that are not picked up are also not showing on the trace so i suspect they are beeing placed on one of the lines that are not physically connected to the card. But i plugged them all in… So it should show up…
Anybody have a clue what to do next? should i disable the two non-used ports on the Diva, and how?