I've heard of cases where a Sephardic family, for whom rice is totally kosher for Passover (assuming it's checked and contains no additives etc.), cooked rice in a pot. The next day, they invite their ...
Prepared mustard (containing vinegar and the like) is certainly not kosher for Passover. According to Ashkenazic practice, the mustard plant itself is included in "kitniot" and prohibited on ...