I've been asked to prepare an amended 2016 1041 to carry back a loss generated in 2017. I'm using ProSystem fx, which doesn't seem to handle Form 1041X very well. The original 1041 was filed 6 months late and so there was a late-file penalty on the original return, which was paid when the return was filed along with the tax due and interest. I've now prepared the amended return but notice that the software is recalculating interest on the original late-file penalty through the date of the amended return expected file date. I'm not getting credit (from an interest due standpoint) for paying the penalty back in 2017 when the return was filed. Is this correct? Thank you in advance for your help with this.