It didn't just happen once or twice, it was happening ALL the time, and it became a bit of a running joke on the trip. The GPS had a very clear view of the sky, but the reception was poor at best, and exceptionally fragile.
Very disappointing - I wish Tomtom had hurried a little more with their release, as I would have bought their product in an instant rather than shelling out 99 Euros on Navigon's second-rate product.