Ipad sound not coming out of dock socket

[djc45]

Hi,
I have the apple dock for ipad 1 connected to my plasma screen using the vga adapter and a 3.5mm audio jack cable from the dock to the pc audio input on the tv.
When I dock the ipad and use the Netflix app, I get the video on the screen of the tv, but the sound still comes from the ipad speaker, despite there being an audio cable plugged into the dock's audio output.
If I move the audio cable from the dock to the ipad headphone socket, the sound comes through the tv, which is what I want.
I assumed that if the ipad was docked the sound would automatically come out of the dock socket. Are there any other settings I need to change on the ipad? Or is something faulty?
Any ideas?

 

[djc45]

I just tried using the ipod app on the ipad, both music and video played only through the ipad speaker, despite the video playing on the tv.
Does anyone think that the dock could be faulty.

 

[djc45]

I seem to have got to the bottom of it.

The sound stops coming out of the dock when the vga adapter is connected, as soon as it is disconnected the sound is routed out the dock line out socket.

Why would apple design it this way so you cannot get video and sound out of the dock at the same time, is seems odd.