There is no shortage of curious behaviour in our parser when you look hard enough:
foo
(note the space at left, this is what I call a 'spaceblock' and renders as <pre>foo</foo>)
<pre>foo</pre> (again with space, renders exactly as before - the parser evidently decides the extra <pre> is redundant)
But what about: foo </pre>
Strangely enough, this renders without a <pre> block at all.
Steve