Timtim:

parawizard:In my opinion it should "It was a man who hit me" in English as well and not using that. It seems to be a gray area historically and I can't really find any definitive rule.

Either works, since the question can be "Who hit you?" (-> "It was the man who ...") or "What hit you?" (-> "It was the man that ...")

This is what I was referencing. For me I would still answer with who, at the very least in writing. I may refer using whichever the person asked with out of spoken reflex. You will run into two camps with differing opinions on the use of that and who but like I said it isn't interchangeable in non-restrictive clauses.

Fenris_kcf's contribution is a very good one - it's certainly an error I've seen on many occasions. "La hundo, *ke* loĝas en la apuda domo ..." etc.

This is exactly the ambiguity I was referring to in my post.