I did say it was a pet peeve of mine. It's just something that has always bugged me for the exact reasons you mention.That's a matter of preference, not a mistake. I realize it's not easy to design a dress with a hole for a tail that's bigger in the middle than at the end attached to the body (doesn't it press her fur back going thru?), but it looks more decent than a design that would expose her underwear with a wag.DCS did make a common mistake all cartoonists make: Millie's tail should be peeking out from under the dress, not poking out from the back of it.
I always figured that instead of a hole for the tail, underwear and pants come with a slit that is fastened with a button. Makes more sense.
As for her tail exposing her underwear, I doubt Millie wears any. Plus, the weight of the dress would keep her from raising her tail too high.