Turbotax "check for errors" will not allow the $600 limit for a joint standard deduction tax return

I am filing a joint return with standard deductions. I have tried entering the donation details, and the total of the donations (above $600) in the 1st box and $600 in the allowed max box but the "check for errors" gives me an error every time. It will only fly if I set the limit to $300. The form actually says "$300 max for single, $600 for joint", but only $300 gets by the "check for errors".

 

And Turbotax does not complete this worksheet form automatically with expected values, even though it has all of the information.  it needs.

 

Wayne U