Retirement tax questions

I am itemizing and TT is recording $300 on line 10b plus my full charitable contribution of $900 on Schedule A. Double counting!

 

I assume line b is either: 

- only for those who are taking the standard deduction or

- my charitable donations on Schedule A should reduce for the $300 that is being attributed to line 10b. 

 

Any thoughts on how to correct this?