I've got a problem where viewing categories (after already having a product in the cart) and selecting to add another of same product resets the QTY back to 1.

Sequence of events:
Add product to cart.
increase QTY
update cart
select categories and pick same product
view your cart and QTY drops back to 1... instead of adding 1 to QTY giving 4.

keep smiling,
Ron

This is caused by setting your default quantity to one in the software under the More Options tab. If you change that to "Let the buyer choose", this will perform the function you are looking for.