worng xsl:sort by numbers?

Hi,

I have a <xsl:for-each select="..."> in my xsl. I want to sort the
elements by the number:
<xsl:sort select="nr" order="ascending"/>
But then I geht the following:

Nr.  Teil
----------
10   test1
110  test4
120  test5
250  test6
40   test2
80   test3


But I need it like that:

Nr.  Teil
----------
10   test1
40   test2
80   test3
110  test4
120  test5
250  test6

Can anyone tell my, what's wrong in my xsl:sort?


greets
John


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