T4A(P) No. of Months disability vs retirement

I have a T4A(P) that contains both Retirement benefit and Disability benefit. It appears that the software expects you to have "No. of Months" filled in for both disability and retirement if this is the case. After calling and confirming with ServiceCanada, they have directed filling in only box 21 (disability) with 12 months. This leads to an error and prevents netfile from working.

 

Is this something I'm doing wrong?