Class 800 lights issue

[Dave_C]

Evening. I have to say I'm stumped on this problem so all thoughts grateful. 

I have one of the class 800s (the Hitachi test train model as opposed to the GWR 5 car model) to which I have fitted two standard Hornby 4 function decoders (R8249). 

My problem comes with the directional lights. The 'front' car works perfectly - white lights when going forwards, red lights when in reverse direction. 

The rear car however is the problem - white lights in both 'forward' and 'reverse' modes. 

I've followed the advice Chrissaf has given to others on here in terms of reprogramming CV29 so that the rear car has a different value to the front car. Based on the online calculator he has suggested elsewhere, I calculate the 'front' car should read CV29 as 34 and the 'rear' as 35 (I have assigned both cars the address of 800). 

Alas, this still hasn't solved the problem. Nor has programming the decoder for the 'rear' car while being sat in the front car's chip slot and then moving it to the rear car as has also been suggested here.  

So, all in all, I'm pretty stumped. For completeness I'm using a Gaugemaster prodigy advance 2 while programming and operating all this. 

Help and views much appreciated. 

Many thanks