It's very funny you should mention that just now, I collect my new car from the factory yesteerday, and this morning bright and early took it out for a quick 20 mile drive, as you do, and found exactl the same thing happening. I had to pull it out very slowly, a bit at a time, until I had enough spare to slot home. I stopped for some petrol after a few miles, and when I got back in, there was no problem whatsoever. Odd. My old Three Wheeler was absolutely fine in this respect.
I notice that my new car now has seat belts that fully retract, and don't leave a short length to flop around, looking untidy. I wonder if the rewind mechanisim is different, and is now more sensitive?