Strange, very strange indeed.
I use VPN at home with an ADSL v1.0 filter plate
It should work as the iplate only isolates the ring wire. You still need to use ADSL filters though!
If you are not scared of the wires behind the faceplate, I recommend a filtered plate.
If you find a solution could you post it, as I am an network engineer and one of our users could run into this one day.