Finally I have managed to validate my product page with the quantity fields and submit buttons on it. What I did was to edit the the includes/form.inc file and generate a random number before each ID and added to it for text fields and buttons. After that I have removed the ID reference from the labels above because they generated warnings (not errors but still unsatisfying) about non-existent ID's. Now I have to do heavy testing to see if this messed up with something else. If you have done that 'random-id' thing before and saw some negative effects, please share.