BUG: Mail search fails to find e-mails in most recent 2 months

Why does Mail exclude the most recent two months from any search I perform? For example, if I search for "lab", Mail finds all instances of e-mails containing the word "lab", but only if those e-mails are older than 2 months. Why would it exclude only the last two (and thus to me the most relevant) months? This looks suspiciously like a bug.