SOLUTION!
Deactivate all ping-o-matic related stuff, XHTML self-checking etc. and comment out with # or two slashes “//” following lines in post.php file in wp-admin directory. Lines are:
199: register_shutdown_function(‘do_enclose’, $content, $post_ID );
200: register_shutdown_function(‘do_trackbacks’, $post_ID);
and
436: register_shutdown_function(‘do_trackbacks’, $post_ID);
437: register_shutdown_function(‘do_enclose’, $content, $post_ID );
It seems that only posts with lots of links are prone to be long posted due to some kind of checking of links. Disable this checking with commenting out those lines and posting happens INSTANTLY!!!
