Within the Wealth and Ratings section there is a place to keep track of Model scores and ratings. When you update the start date to one of these the 'updated on' field changes to reflect the start date.
We are currently evaluating this issue for a fix in a future service pack.
Steps to Duplicate
1. Search for Constituent record 2. Click Wealth and Ratings 3. Click Model Scores tab 4. Note the Updated on Date 5. Edit the 'Test Score' 6. Change the Start Date 7. Note the 'Updated on' Date changes to the Start Date not the date is was Updated on