Wordpress Export / Import doesn't work as expected

When I export some pages from site A to site B with the official Wordpress Importer Plugin, the imported posts on Site B show wrong or no featured images. To be specific, if the post on site A had id 600 and there is a post on site B with that id, the featured image of this post will be taken, instead of the image that came with the exported article.

Similar problems are described here: http://wptavern.com/whats-going-on-with-the-wordpress-importer

Now I have to export 115 pages to 28 sites - can't do this manually. How can I solve this Importer problem?