Do you, by any chance, still have ~/.sven config dir with this problematic configuration?
If so, please archive and attach it here.
Yes. I renamed it, copied the default sven from a nosavefile FD and then restarted, and it worked (albeit without my customisations).
I have since done the same customisations and it works fine. I don't know what the cause is. I think it has something to do with clicking "apply" instead of "ok" as that is the only variation I have made in the way I have done things.