No, many others have found the problem that the software has when you border the 400% mark.
However, you are wrong about qualifying for the Premium Tax Credit. The problem is the when you border the 400% mark, TurboTax does not do things correctly (as you've seen). Interestingly, in my test scenario it works (but I don't have some of your exact numbers, so that could be why.
What is your AGI (Line 3 of Form 8962) if you UNLINK the 1095-A (so the health insurance does not show up on Line 29 at all)?
I can give you a possible work-around, or you could do the exact numbers manually (which is rather gruesome). Or another possible 'easy' fix would be to contribute about $3500 to a Traditional IRA (which may get you under the 400% border).
