We've ripped the PROXY detection out of the 1.7 series a long time ago. The proxy detection was showing it's age, and didn't work quite as well as BOPM. We have been looking into making a replacement module, but found it to be too much hassle to get a decent module for Anope when there is BOPM to do the same, but better.
More information can be found in the bundled docs/PROXY file...