The addition of the class java.net.Proxy (RFE 4696512) can cause a source incompatibility-- if a compilation unit has the following type-import-on-demand declarations:

import java.lang.reflect.*;
import java.net.*;

(and no single-type-import declaration for the name Proxy) and attempts to refer to the class java.lang.reflect.Proxy by its simple name, a compile-time error will occur in Tiger because the reference is now ambiguous (see 4909749 for an example).

This source incompatibility needs to be documented in the compatibility page for the release, like was done when java.util.Timer was added for Kestrel:

http://java.sun.com/j2se/1.3/compatibility.html

The compatibility page is generated from the compatibility sections of CCC requests. The CCC request for 4696512 did not mention this issue in its compatibility section, so please file a fast-track CCC request for this bug to document the source incompatibility.
This incompatibility is documented in the 1.5 compatibility page:
http://java.sun.com/j2se/1.5.0/compatibility.html