For example at the bottom of the java.net package description page

http://download.java.net/java/jdk9/docs/api/java/net/package-summary.html

the "Networking System Properties" link

http://download.java.net/java/jdk9/docs/api/java/net/doc-files/net-properties.html

redirects to the page attached as an image to this issue.

The set of affected packages is likely comprised of those with source code directory trees containing doc-files directories:

jdk/src/java.base/share/classes/java/lang/doc-files
jdk/src/java.base/share/classes/java/net/doc-files
jdk/src/java.desktop/share/classes/java/awt/doc-files
jdk/src/java.desktop/share/classes/javax/imageio/metadata/doc-files
jdk/src/java.desktop/share/classes/javax/swing/doc-files
jdk/src/java.desktop/share/classes/javax/swing/plaf/multi/doc-files
jdk/src/java.desktop/share/classes/javax/swing/plaf/nimbus/doc-files
jdk/src/java.desktop/share/classes/javax/swing/plaf/synth/doc-files
jdk/src/java.desktop/share/classes/javax/swing/text/doc-files
jdk/src/java.desktop/share/classes/javax/swing/undo/doc-files
jdk/src/java.desktop/unix/classes/sun/awt/X11/doc-files
jdk/src/jdk.jdi/share/classes/com/sun/jdi/doc-files