i run into a somewhat strange problem. so i hope i can formulate it properly

i wrote a new linkobject which works as intended. itsmconfigitems are now linked to other configitems, to tickets and to myLinkobject.
On my local installation it works fine and all 3 linktypes show a form like:
http://192.168.73.110/otrs/index.pl?Act ... etID=40698
now i installed the same scripts on a remote location, where it otherwise works fine but results in some strange behaviour:
1) if i access from within the remote net, everthing is ok
2) if i access via vpn and explicitly use https everything is ok
3) if i access via vpn and http i need to login again each time i follow the link to myLinkobject (and next get forwarded to the correct page )
for 3) the links shown are formed like the link below for linkobjects ticket and configitem (and work as intended, even if its prolly not intended to append the same variable three times...)
http://192.168.254.35/otrs/index.pl?Act ... 12594fd0bc
the link shown for myLinkobject is "normal"formed, does not include the agentinterface variable and requires another login if i follow it.
any ideas what causes this behaviour?
br, carsten