The name server configuration is pretty complicated in IPFire. They need to be entered at completely different places for various dial-in options. PPP requires them being set in the profile. RED configured as static requires them being set in the setup program. DHCP uses the automatically assigned ones or allows setting them in the web user interface. I think it makes sense to unify this and move everything to the web user interface with the setup tool allowing to edit them as well.
This is fixed by now.