Valid doctype-system output

Hi -
 
I have the following at the top of my XSLT to output a doctype declaration:

<xsl:output method="xml" indent="no"
doctype-system="http://xml.cxml.org/schemas/cXML/1.2.011/cXML.dtd"/>

With most XSLT Processors I've used (Saxon, MSXML, XMLSpy) this will output
the following doctype declaration:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE cXML SYSTEM "http://xml.cxml.org/schemas/cXML/1.2.011/cXML.dtd">

One XSLT Engine engine I'm using, SAP, outputs the following with the single
quotes and the extra brackets and carriage return:
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE cXML SYSTEM 'http://xml.cxml.org/schemas/cXML/1.2.011/cXML.dtd' [
]>

Is this a valid doctype declaration for an XSLT processor to generate?
They're saying that it's valid based on the XML standard but a number of our
vendors have trouble parsing this. I didn't see anything specific in the
XSLT standard about this.

Thanks,
Jesse