[Plugin WooCommerce] importing products and memory issue

Hi every one.

I have old websites on WordPress 3.5.1 with WooCommerce 1.6.6 with over 9000 products and really old theme but everything is stable. TPC! Memory Usage plugin shows 35M of memory usage.

On the same server in with new database I’ve installed a fresh WP 3.8.1 with newest WooCommerce 2.1 with premium theme. Old database has a lot of garbage and old plugins data. Without any products with only base plugins memory usage is around 30M. After Uploading half of products using WooCommerce CSV Import Suite from old website memory usage is almost 256M! Products are exactly the same like on old WordPress.

Both websites are on dedicated server with 2048M limit. WordPress limit is set to 1024M and WooCommerce is showing that properly.

Why after importing products there is such large memory usage?

Please help me figuring this out.