Conditional formula with summation not returning correct result

Hey everyone! This isn't necessarily a problem persay, as there are other ways of doing what I'm trying to do, but it just boggles my mind why this has worked just fine for years and now it doesn't in this particular case.

Here's what's going on, it's very simple:

______A___________B__________C__________D_______
1)_-$16.00_______-$0.50_______"Total 4"____=sum(A1:B1)
2)__-$4.50________$0.00______"Total 5"_____=sum(A2:B2)
3) ===========================================
4)_=sum(A1:A2)__=sum(B1:B2)__"Total"____PROBLEM CODE


Here's the problem code: =if(sum(A4:B4)=sum(D1:D2),sum(A4:B4),"Error")

The problem is that even though these two sums are equal I keep getting an error back! I've checked for formatting issues, but these are definitely numbers I'm trying to sum up. But since this anomaly is located in such a simple case, I don't really know what else to check for.

Interestingly enough, if you start messing with the values in the spreadsheet I attached you'll get varying results. If B7 drops below -$244.65 suddenly the error disappears! Or if you zero out cell C5 the error disappears. None of this makes logical sense to me. Obviously I don't need to set up my spreadsheet like this, I can do it a different way and thereby eliminate the problem, but I wanna know what in the world is going on here!! Any help would be much appreciated!


frustratingly yours,
-Mike