Looking at the Odyssey source all I can tell is that two string objects are created and their contents are read out when ever the a configuration is loaded, saved or reset. Each string object in the window gets a unique ID to automatically set the contents, i.e. after loading a new configuration. However, I just noticed that in contrast to all other string objects the two in question get the same ID. This definitely causes all the trouble, because one setting will be applied to two objects with different tasks and hence cause the trouble you are experiencing. This can only be fixed in Odyssey.
Here are the some lines from prefswindowclass.cpp:

Child, str_proxyhost = (Object *) MakePrefsStringWithWeight(GSI(MSG_PREFSWINDOW_NETWORK_PROXY_HOST), "", 256, 80, MAKE_ID('S','N','P','H')),
Child, str_proxyport = (Object *) MakePrefsStringWithWeight(GSI(MSG_PREFSWINDOW_NETWORK_PROXY_PORT), "", 6, 20, MAKE_ID('S','N','P','P')),
Child, str_proxyusername = (Object *) MakePrefsString(GSI(MSG_PREFSWINDOW_NETWORK_PROXY_USERNAME), "", 128, MAKE_ID('S','N','P','U')),
Child, str_proxypassword = (Object *) MakePrefsString(GSI(MSG_PREFSWINDOW_NETWORK_PROXY_PASSWORD), "", 128, MAKE_ID('S','N','P','U')),

One can easily see that str_proxyusername and str_proxypassword get the same ID while all the others get unique IDs.

Why the hell are we endorsing this pornographer?