I can't seem to figure this out and I'm sure it's never done this before. I've tried all the texture types (including advanced) but there are no signs. I've triple checked in photoshop and the texture is clearly saved as 512 by 256 but when loaded into Unity it becomes 512 by 512.
???
Also, in Unity 3, select your texture in the Project view. In the Inspector, change the Texture Type to Advanced, and set Non Power of 2 to None to turn off scaling:
The file format you choose will make a big difference. For example PVRT compression requires a square and power of 2 texture and I believe the DXT1 and DXT5 do as well. If you are sure that you don't want Unity to scale your texture, then choose a non-compressed version.