Detail navigation does work with HTTPS

We have developed our own detail navigation based on the Navigation Tag Library

http://help.sap.com/saphelp_nw70/helpdata/en/42/fd510e2aa95277e10000000a1553f7/frameset.htm

My problem is that it works fine with HTTP but not with HTTPS. The navigation links gets generated with the HTTP protocol rather than the HTTPS protocol. Hence, the user enters the portal by HTTPS but as soon as the user click on the links in the detail navigation the portal switch over to HTTP?

Is there anyone that knows why this behaviour occurs and how to get the links generated as HTTPS urls?