Ok, so I have a Fiesta, when I bought it I had a new clutch fitted at mr clutch as the clutch had gone on it. Its been perfect for the last 4000 miles

Now, when I change gear, If I come back on the throttle a bit too quick (before totally releasing the clutch) the engine will stay at whatever rpm it was at before I totally released the clutch until I come off the throttle then it will drop down to the correct RPM, so I took it into Mr Clutch on friday, they checked the clutch and done a road test and found no problem.

So I carried on driving it and today, on the way to work, I was doing about 30mph in 3rd, put my foot down and the revs just increased without accelerating. So I drove to Mr Clutch again and asked them to take a look (by the time I got to Mr Clutch it had stopped doing it) and they found nothing wrong again (maybe because the clutch had warmed up????)

Anyway, they have asked me to take it back in after work tonight so they can take another look. Any ideas on what to say to them / do?