ant regex <mapper> task

Hi,

how do I replace a substring from a path?

I am using

<pathconvert property="to.classpath" refid="from.classpath" >
<mapper>
<mapper type="regexp" from="(.*)bin(.*)" to="\1\2"/>
</mapper>
</pathconvert>

where

from.classpath is

"C:\temp\dp\util\bin;C:\temp\dp\util\stack"

\1

returns

C:\temp\dp\util\

but

\2

does not return anything.

I would like to get back

"C:\temp\dp\util\;C:\temp\dp\util\stack"


Thanks
Stefan