preserving last 32 messages

Can someone tell me what's wrong with the following code? It is supposed to
preserve the last 32 messages, but I currently have over fifty messages in
my backup directory. I am using the following code from one of Gross'
tutorials.

:0 c
backup

:0 ic
| cd backup && rm -f dummy `ls -t msg.* | sed -e 1,32d`