Replacing 3 way switch (horizontal switch) 2 separate 3 ways in one box, each switch has its own power going to it. Top switch two travelers are hot common is not. it seems to work fine with the old switch attached, just curious as to why?
The usual reason is that the installer is moving the wires to the same position on the new switch, rather than looking at the screws' function -- because every 3-way has their screws in different places and the installer did not realize the screw colors are the important part. That's the usual reason.
This is one reason I make a point to positively identify the two travelers and mark them with yellow electrical tape. Yellow wires on yellow screws, there ya go. In a cabinet with two unrelated 3-ways working in close proximity, I use blue, purple or green for the second set of travelers. They sell a 5-pack of 5 colors of electrical tape for about $5 in most stores.