WooCommerce: adding form elements to variable.php breaks quantity functionality - php

Question

I added two extra form elements (radio buttons) within the form of single-product/add-to-cart/variable.php. Now quantity field doesn't work: if I pick "5" for instance, click Add-to-Cart button and visit my Cart, only 1 item was added instead of 5. If I remove my extra elements, it works again. Any suggestion as to what's going on?
I added my form elements right after do_action( 'woocommerce_after_single_variation' ); :
<?php do_action( 'woocommerce_after_single_variation' ); ?>
<div class="auto_replenish_wrap">
<div class="auto_replenish_option">
<input type="radio" name="auto_replenish" value="auto_replenish_no" checked="checked">
<label for="auto_replenish_no">
Deliver one-time only
</label>
</div>
<div class="auto_replenish_option">
<input type="radio" name="auto_replenish" value="auto_replenish_yes">
<label for="auto_replenish_yes">
<div class="auto_replenish_yes_label">
Auto-replenish <a href='#'>(See details)</a>
</div>
<div class="auto_replenish_yes_label_frequency">
<span class="delivery_frequency">
Deliver every
<input type="button" class="minus" value="-">
<input type="text" size="4" class="input-text qty text" title="Qty" value="1" name="quantity" step="1" pattern="[0-9]*" id="delivery_frequency_value" min="1">
<input type="button" class="plus" value="+">
month(s)
</span>
</div>
</label>
</div>
</div>
<div class="add_to_cart_and_learn_more">
<a class="learn_more_after_add_to_cart_button" href="<?php the_permalink(); ?>">Learn More</a>
</div>