Hotmail is always farting around with their filtering system. Sometimes mail get redirected to your junkmail folder and other times it just vanishes - *POOF*
The real problem becomes you don't know what mail you are missing because it never gets to you. If it's something you are expecting or from someone you are in regular twoway communication with, you *may* eventually figure out that one or more emails have gone astray, but if it's a note from someone you don't correspond with often, you'll never know it's missing and they'll be wondering why you don't reply.
Bottom line.. hotmail sucks. Use anything else but.