I guess you want to upload 480p to Youtube or similar? Youtube expects 854×480 for its 480p setting.
It seems that the Sony AVC codec doesn’t correctly handle frame sizes that are not a multiple of 16… at least, that’s what I see in Movie Studio HD 10.
854 pixels is not an exact multiple of 16 (many codecs work on blocks of 16×16 pixels), and Sony AVC doesn’t correctly handle the leftover pixels.
The MainConcept AVC seems to get it right, so you can try using that instead. Depending on your Vegas version, you’ll have different options compared to Sony AVC, but you should be able to adapt an existing template or recreate the Sony AVC templates to get the same kind of output. See https://support.google.com/youtube/bin/static.py?hl=en&page=guide.cs&guide=1728585&topic=1728573 for what video format Youtube expects.
Alternatively, you can modify your frame size for the Sony AVC renders to 848×480 or 864×480… however, that might get letterboxed/pillarboxed by YouTube or similar sites.