According to XSLT 1.0 specification (http://www.w3.org/TR/xslt#copying) "use-attribute-sets" attribute should not be used when current node is a root node, but XSLT processor in JAXP RI 1.4 and JDK 6.0 processes this attribute for a root node. Detailed explanation is given below.

Consider the following code fragment from file attribset27.xsl (attached):
"<xsl:template match="/">
<out>
 <xsl:copy use-attribute-sets="set1">
   <xsl:attribute name="text-decoration">none</xsl:attribute>
 </xsl:copy>
</out>
</xsl:template>

<xsl:attribute-set name="set1">
<xsl:attribute name="text-decoration">underline</xsl:attribute>
</xsl:attribute-set>

<xsl:attribute-set name="set1">
<xsl:attribute name="color">black</xsl:attribute>
</xsl:attribute-set>

<xsl:attribute-set name="set1">
<xsl:attribute name="font-size">14pt</xsl:attribute>
</xsl:attribute-set>"

It produces output presented in file attribset27.out (attached):
<out font-size="14pt" color="black" text-decoration="none"/>
So attributes font-size and color appear in the result due to usage of "use-attribute-sets" attribute:
<xsl:copy use-attribute-sets="set1">
The correct output should look like:
<out text-decoration="none"/>

How to reproduce:
"java XSLTransform attribset27.xml attribset27.xsl"

Detailed explanation:
According to the XSLT 1.0 specification (http://www.w3.org/TR/xslt#copying):
"The |xsl:copy| element may have a |use-attribute-sets| attribute (see [*7.1.4 Named Attribute Sets*] <http://www.w3.org/TR/xslt#attribute-sets&gt;). This is used only when copying *element nodes*."
Difference between root nodes vs.element nodes described in XSLT 1.0 data model definition (http://www.w3.org/TR/xslt#data-model). In fact it refers to XPath 1.0 data model.
XPath 1.0 data model defines root nodes as following (http://www.w3.org/TR/xpath#root-node):
"The root node is the root of the tree. A root node does not occur except as the root of the tree. The element node for the document element is a child of the root node."
So "root node" is an XML document as a whole. Element node is just an XML element, a document element cannot be a root node.
The problem is that in test's template rule is defined as <xsl:template match="/">, so it matches root node, which becomes "context node" for rules defined inside the template, including <xsl:copy> rule.
Since <xsl:copy> rule is applied to the root node, "use-attribute-sets" should not be used, according to the specification.
XSLT 1.0 specification Errata (http://www.w3.org/1999/11/REC-xslt-19991116-errata/) does not have any corrections for mentioned parts of the specification.
According to the XSLT 2.0 specification (http://www.w3.org/TR/xslt20/#copying) "use-attribute-sets" attribute should not be processed for root node too (it is called "document node" there).
Apache Xalan 2.7.0 also has this bug. Saxon 8.8 does not have it.