Can't set "Fax Detection type" and "Fax Destination"

In "Inbound Routes" --> "Fax" tab I'm doing the following settings: "Fax Detection type" to "Dahdi" and "Fax Destination" to "Fax Recipient" with an extension as the fax recipient.

After that I press the "Submit" button and of course the "Apply Config".

When I reenter to the "Inbound Routes" to see if the settings are in place I found that the settings are gone as indicated in the attached screenshot.

Therefore the system is receiving the incoming faxes successfully, but they never end up to my mail as before.