My case was a little different, but I had the same problem answering box 7 in Turbo Tax. I closed a 401(k) that I had with an old company that I no longer work for and roll over the money into a (pre-tax) traditional IRA, so I would not have to pay taxes on this pre-tax 401(k) money right now. I answered "G" to box 7, which was for pre-tax or untaxed rollovers, but Turbo Tax insisted on calling the money a post-tax Roth IRA, and now I suddenly owed more 2018 taxes, which should not have been the case at all. Clearly, Turbo Tax has a S/W problem using box 7 and 1099R's. So, you need to call the IRS help line.
