$500 was already entered on 1040 Schedule A as Charitable Contributions, Schedule A, line 11 shows the $500 contribution total. Nothing appears in 1040, line 10b. Should have shown $300. Itemized deductions were less than the standard deduction. So, it looks like 1040, line 10b is not working in ProSeries.
"Typing" $300 in Line 10b doesn't work. Nothing typed onto the Form 1040 line 10b enters. You can override the blank space in line 10b, BUT line 10c does not do the subtraction of the $300..
Let's face it, Intuit has not finished the programming for line 10b.
This affects a lot of returns where the taxpayer(s) take a standard deduction.
I think your software is not working well. Type any amount in the schedule a cash contributions, that amount will flow to 10a, then type 300 in Line 10b, you do not have to overwrite anything. I have tried many times. And it does the calculations.
It doesn't do the calculations. As you said, "type $300 in Line 10b".
ProSeries should do the calculations for line 10b, if there are figures in Schedule A for Cash Contributions, and standard deductions are used.
This should be simple logic.
Probably, their programmers are working on many other things now with the last minute legislation in December.