It's possible that last year, even with the income stacking, your non-excluded income stayed in the same bracket and did not get pushed into a higher bracket. (It got pushed up within the bracket it was in, but not high enough to cross the upper boundary of the bracket into the next higher bracket.) It depends on the amounts of income and how the income falls in the bracket structure. The only way to analyze it is to look at the details of the tax returns for both years, which we can't do here. If you compare the Foreign Earned Income Tax Worksheets for last year and this year you might be able to see why the effect is different.
