just playing around with v 4.0.3 and having a fiddle with variants, i've set one of the variants to 0 quantity so that it shows out of stock for a colour, size combination, but it seems that the quantity drop down box goes like it's had too much billy whiz, have a look at the url and choose colour blue , size 34 and you will see what i mean!!!! any idea what might be causing this
http://www.justhom.com/product.php?productid=1&cat=1&page=1