Post/Page editor loads twice

No, this is not a normal behavior. Try to set default editor, and that should fix it. If it does not fix the problem, you may have one of your plugins causing it. Deactivate all plugins, and then reactivate them, one by one, until you find one, which is responsible. Code below goes to functions.php:

Set default editor to HTML:

add_filter('wp_default_editor', create_function('', 'return "html";'));

Set default editor to Visual:

add_filter('wp_default_editor', create_function('', 'return "tinymce";'));

Update: the proper use of a closure, will be:

add_filter('wp_default_editor', function() { return 'tinymce'; } );