>  <xsl:template match="@xmlns:xsi" />

> to be a bit of a special case. However whatever I try isn't helping: the
> xsi:noNamespaceSchemaLocattion attribute is being dropped, but the
> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" attribute is not.

It's not an attribute... just add exclude-result-prefixes="xsi" to
your stylesheet




--
Andrew Welch
http://andrewjwelch.com
Kernow: http://kernowforsaxon.sf.net/