Scaling of Reference Attachments When Attached Changes Itself

What is it that changes the scale of reference files when I initially attach them? This morning I attached two files, both at 1:1 scale. The first came from an AutoCAD export. Somehow it acquired a craving for metric units. I attached it, it came in to the next county over (waaaay over there), and when I checked the scale it had changed itself to 1:3.2808. The next file I attached changed its scale from 1:1 to 1:10, so it was in another state when it came in.

What is responsible for this? How can I avoid it in the future? I don't mind the occasional miscue because hey, it happens, but two for two to start the day? I had the same thing occur numerous times last week with various files.

thanks. mstn V8i SS3