Hm, that code works fine for me as-is, but I don't know what Joomla/xtypo may be doing with those {xtypo_button1} tags exactly -- you might try moving those inside the anchor tags, like so:
<a onclick="javascript:return EJEJC_lc(this.parentNode);" class="ec_ejc_thkbx" href="#">{xtypo_button1}Add to Cart{/xtypo_button1}</a>
The href="#" makes the anchor tag act like a link (e.g., so your CSS will style it like your other links, and the hand cursor will appear when hovering over it) without having it actually function as a link to another page (the # would normally be followed by an anchor name appearing elsewhere in the same page, to make a link that jumps to that point in the page), but you can try removing the href="#" to see if that helps your situation.
