msxsl saxon exslt power function

A general question ...
Using saxon 6.5.3 with the math namespace the following works beautifully:
   <xsl:value-of select="format-number(((math:power(1.95, (1 div 8.5)) - 1)
* 100), '#,##0.00; -#,##0.00')"/>
and I get the output 8.17.

However when I used msxsl 4.0, the error "math namespace does not contain
any functions". So I downloaded the exslt functions added the line
<xsl:import href="math.xsl" />
and changed the <xsl:value-of ...> statement to 

<xsl:call-template name="math:power">
   <xsl:with-param name="base" select="1.95" />
   <xsl:with-param name="power" select="1 div 8.5" />
</xsl:call-template>

and the error "xslt template math:power doesn't support fractional or
negative arguments". I'm just wondering why is there a difference in
functionality? and is there some other function/way of getting this to work
with msxsl?

Thanks,

Dan Whitney