First thing that I did I got unexpected Results. I set my prefernces for still images to 1 frame (at 29.97) and dragged 30 pics to the timeline and Vegas has a freme of black (every two pics) nothing that Excaliber won't fix, but still, this is not ...Just got the same result in v8. Hmm.
If you are trying to bring in an series of images for an animation use File>Import>Media> select first frame and then select open still image sequence.