Retirement tax questions

The amount on line 22 form 104 AD is 24,490 the amount of my taxable SSA line 3.  It’s interesting- the amount on that form line 4- primary taxpayer pension, annuity, IRA income is 0 calculated as 20,000 less the 24490.  Do they assume that no one would have Social security greater than. 20,000??? There is a problem with the program.