My Lacey is 5 months old and her tail is curled. Don't know anything about a straight tail. Maybe you should call or email the breeder and ask her about the tail. Maybe this is a common trait in her/his maltese. Just a thought.
hopefully there's a breeder that posts about it. i have no idea what their tails look like when they're under 13 weeks. but i remember on Newlyweds: Nick and Jessica simpson...on MTV, they saw someone, it was DivaPups....anyway, their tails were straight. i thought it was weird, but people on MO say that their dogs tails are straight too. anyway, thats the info i have, i hope it helps a little.