Following XSL causing strange HTML errors

<div id="typeDiv">
	<xsl:choose>
		<xsl:when test="1=1">
		</xsl:when>
	</xsl:choose>
</div>

Something about the above code is causing an elusive problem with the
HTML in my document. Removing the code removes the behavoir. The above
code, as far as I can tell, should have absolutely no output (although
it may have whitespace, someone else could tell me).

if I place <xmp> inside the div, encapsulating the XSL, a quite
strange thing happens. The code for the close-div tag appears, as well
as the rest of the document after the div as though the XMP tag were
not closed.