Thank you for your explanation, but unfortunately it is not of much use. I'm asking if this is a bug in the firmware, as I own an RUT950 (also in bridge mode) and there are no problems accessing the LAN configuration page on it.
As I said there are valid reason why you would want to access the LAN config page while in bridge mode (again, to clarify, clicking on then Network > LAN menu does not show the LAN config page, instead it shows the Overview page). If I take the modem out of bridge mode, then I can click on Network > LAN and the page is displayed as expected.
Note that I am not talking about accessing the modem's web interface while in bridge mode, this is specifically the Network > LAN page within the web interface that is not accessible while in bridge mode.