The amount on the "Other Taxes" line on your return is Additional Medicare tax, which is unrelated to your 403(b) contribution. You can see this by previewing your 1040 and scrolling down to Schedule 2. The $1,400 will be on line 11, Additional Medicare Tax. To preview your 1040, follow the same steps you used to view the summary. You should then see an option on the left panel that says "Preview My 1040".
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