i know that with Lacerte you need to populate the 1040x BEFORE you make any changes to the original return.  It looks like the same process with ProSeries https://proconnect.intuit.com/community/amend-tax-return/help/how-do-i-amend-an-individual-return-us... Notice that the very last step #12 is where you finally make the changes to the return. 

If at first you don't succeed, try, try again.