the answer depends on what characters can "keyword" be composed of. I'd think that only letters a-z A-Z (+ numbers, if you specify in the setting) are considered. So it means that your "a/c" was not keyworded, and therefore cannot be found by typing only a/c, because that kind of search searches only for keywords (in this case in the user defined keyword attribute). If you enclose it in the double quotes, that is a phrase search, ie. brute-force
