looking at the code on your page, there are multiplle form tags around each element, there is a form around the submit button:
<form name="eCart1_1_ATC_<?php echo $row_WADAProducts["ProductID"]; ?>" method="POST" action="<?php echo $_SERVER["PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".$_SERVER["QUERY_STRING"]:""; ?>" valigh="bottom">
<input type="hidden" name="eCart1_1_ID_Add" value="<?php echo $row_WADAProducts["ProductID"]; ?>" ><input type="text" name="eCart1_1_Quantity_Add" value="1" size="4" /><input name="eCart1_1_ATC" type="image" class="eC_ImageButton" value="Add to Cart" src="../WA_eCart/Images/Desert Spice/Btn2_EN_addtocart.gif" alt="Add to Shopping Cart" border="0" /></form>
a form around the size label:
<form id="sizes" name="Sizes" method="post" action="">
<label for="select"></label>
</form>
but no form around the size select list.
this means that when the submit button is pressed, the only thing submitted to the server, is the submit button.
looks like the add to cart button code was edited after it was applied to the page.