Ford focus1.6tdci revving when changing gear

[Kcg1987]

Hi I purchased a Ford focus 1.6tdci zetec sport the other day but when it comes to driving the car I'm absolutely useless. The wee change gear indicator light works and when I go to change gear I lift my foot of the accelerator and push down on the clutch the car revs go up as if I have hit the accelerator, its pretty annoying as you can imagine. I have had the car one day now, but there is the odd time the gear change indicator just stops  when iv been driving a while and the car drives a dream with it off, just drives like a normal car if that makes any sense no over revving or anything. It's like when it's on its assisting me with the gears and making it difficult to drive, even if I ignore the light and change gear at maybe 3000rpm the revs still go up when changing gear then the car jumps as if I have let the clutch out to fast, it's really putting me of the car.

any ideas what could be wrong?