Hi there,
When you click and edit the quantity with a value like "10" it doesn't always work, I've made a video to show the problem as it would be very hard to explain, see https://www.youtube.com/watch?v=ocRJYcQJ_E4 (admin feel free to remove after viewing)
Also notice how I went through to the checkout page when it didn't work and the products weren't in the cart.
I'm using VM3.09
Thanks,
Richard