Are you sure this is right, I read the link and it seems to me that the problem is if you have an IRA of pretax money (like converting from a standard 401k) It’s just too complicated.[/quote]
Yes, I am quite sure it is correct. You can have an IRA funded with pretax and post tax income (not a good idea to mix, but you would be responsible for tracking the amounts – IRS form 8606). Coronita is right that the withdraw from IRA portion of the Roth rollover is treated as a distribution. The tax basis has to be calculated. If the money was placed into the IRA post tax, the basis/initial funds are not taxed on withdraw.
See also: https://rodgers-associates.com/newsletters/how-to-avoid-being-double-taxed-on-your-after-tax-ira-contributions/