I am using the html macro to open e.g. Google in a new (browser-) window:

{html}
<a href="http://www.google.de/" target="_blank">Google-Link</a>{html}

After typing the macro and changing the mode from Wiki Markup to RichText and vice versa
all html-Tags are missing (in Wiki Markup mode):

{html}
Google-Link{html}

After saving the page you have defect html-tags!
If a page contains a lot of text and also a html-macro this will not be recognized by the user.