I entered a SSA-1099 reflecting a benefit received from my parents death. Federal Refund then decreased by more than the amount listed in box 5 on the form.

When declaring the amount received from a parent's Social Security death, the Federal Refund that TT calculates decreases by more than the amount that we received.  In other words, it appears that the SS benefit actually cost us ~ $80 ($280 benefit, but $360 tax increase).  Does this sound right, or am I entering this incorrectly?