Try reducing your 18.3 Mbps bitrate to 4-5Mbps with 2-pass VBR interlaced procedure…this might help. I also encountered this glitch when I saved my project output in the desktop. Maybe your output was saved in a low-storage partition.
If you want a better render output in full HD (1920×1080) in DVD or Bluray, you may use Vegas Pro 11. Studio HD Platinum 11 does not give a better quality output, per my tests; and the “Product Comparison” does not tell the detailed facts.