Turbotax is recording a different dollar amount for my taxable pension on the 1040 line 4b vs. what i entered in the software. IRS is now saying i have underreported?

Example: i entered form 1099-R taxable amt of $20146 in software but the filed return is showing $9688 for taxable amt on Line 4b. why would the amt I entered in software be different than the amt shown on the filed 1040?