IE p tag problem when insert in another tag p

In IE 7 and IE8 (that i test with myself)
It will render not cerrect like this sample
<p>c
<p>a</p>
<p>b</p>
</p>

in source it look ok but in IE render view is
<p>c</p>
<p>a</p>
<p>b</p>
</p>

the thing i want to tell is don't try put tag p in another tag p change outer tag p to div
it will ok.