Please describe the problem:
When creating an attribute by copying the value of the attribute xmlns:xsi (or xsi:schemaLocation, etc.), the result becomes xmlns:xsi1 (or xsi1:schemaLocation, etc.).

Steps to reproduce:
1. Add an XML document like 
<?xml-stylesheet type="text/xsl" href="test.xsl"?>
<TEI xmlns="http://www.tei-c.org/ns/1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.tei-c.org/ns/1.0 tei_minimal.xsd">
</TEI>
2. Add such a template to a stylesheet:

<xsl:stylesheet xmlns:html="http://www.w3.org/1999/xhtml" xmlns:tei="http://www.tei-c.org/ns/1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" exclude-result-prefixes="tei html" version="1.0">
	<xsl:output method="xml" version="1.0" encoding="UTF-8" omit-xml-declaration="no" standalone="no" indent="yes" media-type="application/xml"/>

<xsl:template match="/">
    <xsl:apply-templates/>
</xsl:template>

<xsl:template match="*">
<xsl:element name="{name()}">
<xsl:for-each select="@*">
    <xsl:attribute name="{name()}">
        <xsl:value-of select="."/>
    </xsl:attribute>
</xsl:for-each>
<xsl:apply-templates/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>

3. Transform

Actual results:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<TEI xmlns:xsi1="http://www.w3.org/2001/XMLSchema-instance" xsi1:schemaLocation="http://www.tei-c.org/ns/1.0 tei_minimal.xsd">
</TEI>


Expected results:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<TEI xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.tei-c.org/ns/1.0 tei_minimal.xsd">
</TEI>


Does this happen every time?
Yes

Other information: