TurboTax calculates the amount of your refund, or additional taxes owed based on the information that you entered into the program. When the IRS and/or your state receives the returns, they compare what is on the return to what they have in their system for you.
When they make adjustments to your return it is to account for the difference in what was reported on the return and what they are showing in their system.
You can call the IRS and speak to a tax representative about what was changed on the return and why.
How do I contact the Internal Revenue Service (IRS)?