Well here is how you work around the issue.
Open the config/tinyMceConfig.config and add the lines 5 and 6 to your config:
<!-- this area is for custom config settings that should be added during TinyMCE initialization --> <customConfig> <config key="entity_encoding">raw</config> <config key="spellchecker_rpc_url">GoogleSpellChecker.ashx</config> <config key="relative_urls">false</config> <config key="convert_urls">false</config> </customConfig>
Please note that this only fixes the issue partly. It seems like Umbraco does a convertion on save. My solution was to link to the url without www.