Why TT requests I enter "foreign source amount" only during error check?

Why does TT requests that I enter "foreign source amount" only during the error check, given that it did not request it during the stepwise interview nor ever before. I had similar tax returns for the past 2 years (1099-DIV Worksheets had no amounts entered in "6d") and resulted in no errors. Can you explain why it needs to be entered this time?