I appears that the Quote Product Tax Calculation is broken. To clarify, I noticed that on on both existing and write in products, the extended amounts were wrong if I took the effort to add line-item tax amounts within the quote form (which is ridiculous as a requirement). The Extended Amount field subtracts the tax field from instead of adding the tax field to the amount field for a total. This appears to me to be a clear bug -if I put a negative figure into the Tax field, the Extended Amount is correct. Please feel free to test and confirm this in your environments -I'd love to know your experience and get this fixed my MS if it is indeed a bug.
These are my examples -same results with write in or existing product.