html change on switching from "source" to "normal" mode?

Hi
I cannot understand.
Click the "source" button.
Write this html
<a href="#">
<div>
<p>Foo</p>
</div>
</a>
Re-click on the "source" button to get in "normal" mode.
The html is:
<div>
<p><a href=""Foo</a></p>
</div>

It is possible, I guess, to preserve the exact html you write, isn'it?

How?
Am I doing something wrong?
Thank you.

Pietro Conconi