From dooglus on the forums: https://bitcointalk.org/index.php?topic=47586.msg610456#msg610456

I found a way to make the release candidate crash:

1. use bitcoind to send to an address that's not in the address book
2. in the client, right click the greyed-out address in the 'address' column of the transactions tab
3. 'edit label'
4. the address field is blank - would be nice if it was populated automatically. type or copy/paste the address in, and type a new label name
5. click 'ok' and get a segmentation fault