Belkin surgemaster

I have the Belkin Surgemaster gold and am having a problem with the phone connections on it, I have got a feed into from the main phone socket via my ADSL filter and then I am running my house phone and the SKY HD box from the 2 phone outputs.  The problem is if the SKY HD line is connected then the phone is constantly engaged - has anyone else come across this as it driving me mad having to keep plugging in the SKK HD line whenever I want to access box office etc.

Thanks

DAmian