Can't use variable as temporary tree in XSLT 2.0

This is something I must have done a hundred times, but today I keep butting my head against the wall.

I'm using XLST 2.0 (Saxon 8.7.3j).

I've stripped it down to the simplest example I could imagine and tried with that, but I still don't get what I expect.

In my stylesheet, in a template, I have this variable defined:

<xsl:variable name="months">
  <months>
    <month>JAN</month>
    <month>FEB</month>
  </months>
</xsl:variable>

Immediately after that I have this:

<tr><td><xsl:value-of select="$months/months/month[position()=1]" /></td></tr>

In my result document I expect to see:

<tr><td>JAN</td></tr>

What I get is:

<tr><td></td></tr>

Please someone tell me what I don't see.

Thanks.

-- 
Charles Knell
cknell@xxxxxxxxxx - email