Warning that the bug is back (or never left). I filled out my taxes about 2 months ago and everything worked just fine. When I came back today to update a few forms that came in late I lost my interest deduction. Seems to come down to how you answer the "Did you use your loan for anything besides paying off the existing loan?" If you answer no, the interest gets calculated as zero. On the plus side, if you answer yes and then say "Yes, I've used this loan only on the home I took it out on," then you can get your interest deduction back and calculating correctly. Quite rough and would have cost me several thousand dollars if I hadn't caught it. Went back through past returns and never had this issue but it's going to cost me a few hours to double check everything now that I know a bug like this has been lurking for years.