No, it shouldn't be normal, but it frequently is. Not all MPEG encoders are created equal and you'll get varying results with different encoding applications. Generally speaking, the lower end apps don't offer much scope for tweaking the encoding process. Try encoding your AVI to MPEG2 using TMPGenc using one of the default templates, then use ifoedit to create the VOBs and your buring app to put them on DVD. Search the forums to find a guide to ifoedit.