1040X Line 16 - Source?

Hello.

I am amending my return, and entered the forgotten 1099-DIV which increased my income and taxes.  There is a number showing up on Line 16 on the 1040X, an amount that says I paid with "my extension" or paid with my original filing, or paid after my return was filed.  I didn't pay anything -- I was getting a refund and still am, although a lesser amount (I'll have to pay a little back).  This mystery amount is showing up on the 1040X that I'll need to efile, and it is deducting from the refund amount shown in green - showing it to be more than it should.  Could someone tell me the source of this entry, where I may have entered it in a questionnaire, so I can go back and investigate? I don't believe I did enter anything, but things do happen.  Thanks!