Output Encoding via <xsl:result-document>

I've inherited a XSLT 2.0 transformation that outputs a CSV file using the
result-document instruction like so:
<xsl:result-document href="blah.xml" method="text">

On my computer, the @method setting resulted in a text document encoded in
CP-1252 (according to the Oxygen XML Editor). But the source document for the
transform is XML in UTF-8 and I'm getting reports of unsupported characters in
CP-1252. I want to change the encoding to UTF-8 to support all characters. So
I changed the result-document instruction to be:
<xsl:result-document href="blah.xml" method="xml" encoding="UTF-8"
omit-xml-declaration="yes">
And according to Oxygen the output encoding is STILL CP-1252 and it won't open
the file due to unsupported characters. I've checked the encoding with various
other apps (like NotePad++) and they say the encoding is UTF-8.
Something weird is going on that I don't understand. Why isn't the encoding
instructionB encoding="UTF-8" having effect?
Thanks,
Don