The EVAP system works in the following way. I am open to correction. When the engine is cold, the purge valve is commanded close by the ECU. Once the car reaches operating temperature, the ECU commands the purge valve to open. By opening the valve the intake manifold vacuum is able to pull the fuel vapour through the carbon canister. What is happening in your case is that with the driving of your car the fuel sloshes about in the tank and builds up pressure much like shaking a bottle of cola. The pressurized vapour is not finding its way to the inlet manifold to be burnt up in the engine.
So what could be wrong. Here are a few ideas.
1) We have esablished that the purge valve is healthy and we have established that pipes from the fuel tank to canister and canister to purge valve are clear. So is the ECU commanding the purge valve to open? Back probe the connector to purge valve grip to see if you get voltage at operating temperature.
2) Is the ECU able to read the temperature sensor so that it can command the purge valve to open?
3) Is the integrity of plastic pipe from the purge valve to the inlet manifold good?
If you had a smoke machine, I would have suggested to test the piping from the inlet manifold, through the purge valve, to through the canister up to the connection of the fuel tank
