WordPress XMLRPC API strips out leading angle brackets when posting from an application that uses it such as Scoop.it. This is the reason why your posts appear as html code.
Here’s what you can do:
1- Use this version PHP 5.2.9 (or a higher one) with this library libxml2 2.7.3 (or a higher one). So see if your host will do that for you.
2- Click on the link below and download the plugin: http://wordpress.org/extend/plugins/libxml2-fix/