[xsl] error/confusion with translate function

[Duane Gran <dgran@xxxxxxxxxxxxx>]

XSL Experts,

I'm getting some odd behavior from the translate() method.  I'm using  
it, along with Saxonb 8-7-3j, to convert the value of an attribute  
from upper case to lower case.  Below is the relevant line from my  
source XML:

<desc id="songsie.y.illbk.42" dbi="songsie.Y.P42">

My XSL is defined as the following:

      <xsl:variable name="thumbnail-mixedcase" select="@dbi"/>
      <xsl:variable name="thumbnail" select="translate($thumbnail- 
mixedcase,  
'ABCDEFGHIJKLMNOPQRSTUVWXYZ','abcdefghijklmnopqqrstuvwxyz')"/>
      <nines:thumbnail rdf:resource="http://www.blakearchive.org/ 
blake/images/{$thumbnail}.100.jpg"/>

My resulting document has has "...songsie.x.p42..." instead of  
"...songsie.y.p42...".  Below is the output:

      <nines:thumbnail rdf:resource="http://www.blakearchive.org/ 
blake/images/songsie.x.p42.100.jpg"/>

I'm dumbfounded by this, especially since it works for well over a  
thousand other cases.  I've looked at this closely with the debugger  
in oXygen, but I can't make sense out of how the translate function  
is converting "Y" into "x".  Can anyone shed light on this?

Duane Gran