Hudson doesn't save the setting "TCP port for the JNLP slave agents" if
settings in the Access Control section are not modified.

Procedure to reproduce this issue:
1. Click the menu [Manage Hudson]
2. Click the menu [Configure System]
3. Click the checkbox [Enable security]
4. Select the radiobutton [Fixed] and input an appropriate value
to the text field in the setting "TCP port for JNLP slave agents"
5. Press the button [Save]
6. Click the menu [Manage Hudson] again
7. Click the menu [Configure System]
8. Click the checkbox [Enable security]
9. You can find that the setting in the "TCP port for JNLP slave agents"
is not saved