Resolved! The theme contained an override.
function edit_price_display() {
global $product;
$price = $product->price;
$price_incl_tax = $price + round($price * ( 21 / 100 ), 0);
$price_incl_tax = number_format($price_incl_tax, 0, ",", ".");
$price = number_format($price, 0, ",", ".");
$display_price = '<span class="price">';
}