well, the behavior I was seeing:
add "2" to the first t-shirt entry (white -large) leave the others blank...
You get alerted that values must be entered into the other fields (not very descriptive).
Enter "0" into the other fields... (I liek the shirts, just only need the 2 white large for now).
Select "Add to cart" next to the white large... page refreshes... go to the cart, the shirts are not added.
(I did successfully add the playing cards, so I know it has "something")...