Since that is the case, then the OP can go to menu > settings > video settings > SD Override, and select stretch to stretch the image.
Just throwing my kudos into the hat for this solution .... these are the exact steps to fix this! I upgraded to FIOS (for the second time) about a month ago and have been doing the manual screen size change via the remote (# button) since then... the problem with that method is that it changes back to standard def dimensions every time you change the channel... the steps above gave me +2 sanity points back. Thanks!!
..."the OP can go to menu > settings > video settings > SD Override, and select stretch to stretch the image."
Mine doesn't have an "SD Override" option. The STB Help section says there should be a "Format" option for changing the aspect ratio, but that option isn't there either. The only option under "Video Settings" is "RF Channel".
Is there no way for me to fix this problem?