OK, have managed to get an unrelated crash from starting minetest now with the
mentioned patch so at this point I think that case is unrelated. (Certainly
seems to be more subtle, this MT crash has never been as reliable to trigger as
some of the other things on this thread).

Will endeavour to file a bug separately. Any suggestions on information to
kickstart such a related bug would be appreciated, else I will reach out to
various channels on freenode first to get that ball rolling.