Custom resolution works until you close rikdev. When you relaunch and try a map it ignores the custom resolution. For example my custom res is 1024x768 not fullscreen. When I reboot rikdev and try a map it launched in 1280x960 fullscreen. If I open the settings tab and then try again it's fixed.
To reproduce you probably need an autoexec.cfg aswell with a different setting to the one used in rikdev. (my normal res is 1920x1200 fullscreen)