I just think the team did a good job from what I’m reading. This inconsistency doesn’t impact the top 1% household (who commonly use larger loopholes to avoid taxation at magnitudes more significant than this inconsistency like using loan against assets which they can write off interest against taxes instead of paying taxes to the government). This quirk impacts households in the 2% level for just one fiscal year or more where they might just have a taxed event like a real estate sale (non reinvested primary within the timeline), a taxable equity grant (that the pay taxes on but may lose), one time capital gains from investment sales, etc.

Tax law is supposed to be consistent and fair in general, and the introduction of the Big Beautiful Bill created a weird quirk here, that gets quirkier that you can file separately and correct to jointly but not the other way around legally right now. From 2018–2024, the tax code was consistent on SALT, then in 2025 and looking forward to 2029 SALT taxation becomes inconsistent under certain joint filing conditions that impact a non-trivial number of households especially when it starts at $250k each, or a lopsided earnings of that combined amount and peaks at the $600k.

This team is identifying a pretty big quirk that goes against the principle of consistency in tax law and did a very good job of it applying formal logic to law if they prove this to be correct. Others have done too before AI (which is what your tax software is conservatively doing), but it’s just easier now with AI.