Create a file in Photoshop at 300dpi with a clipping path, import the file into Illustrator CC and place it. Make a note of the scale it imports at then import that same file without a clipping path and you'll get a different scale.

It seems Illustrator is treating the clipping file the same as an embedded file and using 72dpi as it's default resolution.

Why a clipping path should do this to a file is very strange.