after upgrade 3.0.14 to 3.0.16,
my own customfield plugin only can update to cart in "addtocart" position,
if in other position,customfield can't update to cart page:
<?php echo shopFunctionsF::renderVmSubLayout('customfields',array('product'=>$product,'position'=>'example')); ?>
so, is customfield change any rule in 3.0.16?
Found another solution
It must be within the form, which is described in /sublayouts/addtocart.php