Form 1040 line 25 c or Tax payments form question

Hello,  

I am filing Married Filing Separately. I was filling out info for this year's return and my refund increased significantly which I would be happy to receive! I don't have many changes since last year so I compared it to last year's tax and saw that there is a difference in subtraction vs addition in tax payment area.  Just for simplicity, I'm using same values. Last year, line 25a $19206, line 25c  $-4023, Line 25d = $15183 (so last year, it subtracted).  This year, Line 25a $19206, Line 25 c $-4023, Line 25d= $ 23229 (this year, it added).  Since I live in community property tax state, I figured tax payment should much my husbands which would be $15183. Is this a software error?  I spoke with customer service but was not helpful...  Could someone help me figure out if it is supposed to be addition (even though there is negative value) or subtraction?