Filter Chain not working

I have set up 2 cups filters in my PPD file. When I print only the first filter 
is executed. The first filter is the bash script show below:

As I forward

--------------------------------------------------
*NickName: "Canon S400"
*cupsVersion:   1.1
*cupsManualCopies: True
*cupsFilter:    "*/* 0 prefilter"
*cupsFilter:    "application/pdf 0 
/System/Library/Printers/Libraries/PrintJobMgr/Contents/MacOS/PrintJobMgr"

*% Paper Handling ===================
*OpenUI *PageSize: PickOne
*DefaultPageSize: na-letter
--------------------------------------------------
#!/bin/bash
date >> /tmp/prefilter.log
echo 0 $0 >> /tmp/prefilter.log
echo 1 $1 >> /tmp/prefilter.log
echo 2 $2 >> /tmp/prefilter.log
echo 3 $3 >> /tmp/prefilter.log
echo 4 $4 >> /tmp/prefilter.log
echo 5 $5 >> /tmp/prefilter.log
echo 6 $6 >> /tmp/prefilter.log
cat $6
--------------------------------------------------
How can I call the second filter specified in the PPD file ?

Thanks
Alex