After some investigating, I found out that this is happening because when we execute `fur''` in the interactive interpreter there is an implicit newline, which means that EOF does not get reached.
OTOH there is no newline when passing it as a string inside an `eval` call. After the tokenizer encounters the first quote, it calls `tok_nextc` twice more, in order to differentiate between a single-quoted and a triple-quoted string, thus reaching EOF and proapgating an EOF error up through the `perrdetail` struct.