We have a user macro to e. g. change the background color and such things:

span (with body):

#set($wiki=$body)
#set($type=$param0)
#set($arg=$param1)
##

1. 1. The following currently does not work
      ##set($globalHelper=$action.getGlobalHelper())
      ##if($content)
      ##set($renderer=$globalHelper.getWikiStyleRenderer())
      ##set($context=$content.toPageContext())
      ##set($xhtml=$renderer.convertWikiToXHtml($context, $wiki))
      ##else
      ##set($xhtml=$globalHelper.renderConfluenceMacro($wiki))
      ##end
      <span $type="$arg">${body}</span>##

Using this macro in Wiki Markup:

{span:style|background-color:red;}Hello{span}

,

{span:style|background-color:red;}Hello{span}

And then later be edited in RichText will result in:

{span:style|background-color:red;}Hello{span}

,

{span:style|background-color:red;}Hello{span}

Which is obviously different from the expected result. There are other examples where Rich Text easily broke layout, so we currently decided to turn this feature off