I am using a JVC GY-DV500. When I capture tape from it, Vegas capture identifies the video as progressive, but it is actually interlaced, bottom field first. When I capture using a Datavideo DAC100, the video is correctly identified as being 30i, bottom.
Vegas has been doing this occasionaly to me since v3. Sometimes it captures correctly sometimes progressive... I reported this to sonic foundry, but no help. If I ever have trouble with a clip, it's the first thing i check. Change the setting onthe clip property and all is fine.