In Debian at least, with package resolvconf installed, /etc/resolv.conf 
is a symlink to /etc/resolvconf/run which itself is a link to 
/run/resolvconf. It's updated dynamically and automatically. Maybe 
unsuccessfully if your router is flaky.

If you want to edit manually and want it to stick you can rename 
/etc/resolv.conf (the link) to disable it then create a new one with 
custom settings (I do, and use opendns)

https://en.wikipedia.org/wiki/Resolvconf

Not a lot to do with what desktop you run.

D