The drop-down list of modes of operation is again populated with all of the modes that PHP's mcrypt uses. Similarly, the disabled options have not been implemented in this class. I do not plan on implementing ofb (8-bit) as this is considered insecure by NIST. Stream is the mode used for stream ciphers and as no stream ciphers have yet been incorporated, this mode has not been coded.
Changing any option except the cypher texts will trigger the encryption with the new options. Changing the cypher text will trigger decryption. The php verification will only occur by submitting the form. If you're curious as to how the php is implemented, the source for this page is available on the Google Code page for this project.