When editing any kind of text, turn of the Rich Text Editor and type:
        
<!-- <a href="/">-->
<b>this is very important</b>

Then you turn on the Rich Text Editor and afterwards turn it off again and you get: 

<!-- <a href="/" mce_href="/">-->
<strong>this is very important</a>

Or another example: 

<ul>
<li><!-- <a href="/">-->this was link 1</li>
<li><!-- <a href="/">-->this was link 2</li>
<li><!-- <a href="/">-->this was link 3</li>
<li>this is important</li>
</ul>

And we get: 
<ul> <li><!-- <a href="/" mce_href="/">-->this was link 1</li> <li><!-- <a href="/" mce_href="/">-->this was link 2</li> <!-- <a href="/" mce_href="/">-->this was link 3</li><li></a></a></a>

The issue appears especially when various people (from different backgrounds) work on the same document. For sure comments might not be necessary for everybody but nevertheless the Rich text Editor should be able to handle comments correctly.