It records to NTSC (CCIR601?)on the DV tape. By definition, this format is 30 fps(actually 29.97 fps). In order to take the native 24fps recorded by the image sensor, and turn it into 30fps, the in-camera software adds extra frames in either the 2-3 or 2-3-3-2 pulldown format.
Vegas is smart enough to detect 24fps that has been converted to 30 fps; and, will remove the extra frames if you have the right switches slected in “preferences”, returning your captured video to the original 24fps.