I have the same tv w/ a tivo S3, and it should not work that way. You should be able to set the tv's aspect control to "full" and then never touch it again.
When I watch 4:3 SD, there are black bars on the sides. I think the TV is smart enough to remember different aspect settings for different types of content, so you may have to set the aspect on the tv to "full" for various channels, but you should never have to do it again. I never touch the aspect control on the tv any more. The only time I need to adjust aspect is when I'm watching letter box programming on an SD channel - but for that I use the S3's aspect control.
One thing to watch out for though is this: when I first got the tivo set up I had to tell the sony to change the aspect to "full" a couple of times before it worked correctly on certain channels. I'm not sure what it was - certain SD looked wrong... like too squashed, with the tivo info box going off the top of the screen.
Hope this makes sense (and helps).