I understand the double taxation part. NY and CT will tax the telecommuting days. That's not the issue.

What I don't understand is the following math in Lacerte:

Wages from all sources $50,000

Of the above total wages amount earned in CT residency period from NY + CT sources $20,000

Wages from Telecommuting days during residency in CT $5000.

1040AW shows:

Column A $50,000 + $20,000 =$70,000

Column B $20,000

Column C $50,000

Column D $0 (correct)(CT sourced income while NR)

CT-SI shows $20,000

1040 PY/NR shows:

CT Federal AGI $50,000

CT additions to AGI $20,000

CT tax calculated on $70,000 total earnings. 

CT sourced income $20,000

Income from NY sourced $15,000 for tax credit

That doesn't seem right. Taxpayer did not earn $70,000 in the tax year. Anywhere I put the CT resident earnings is adding to Federal AGI and tax is being calculated on it. If I allocate on the State tabs or the Federal wages tabs is changes the Federal AGI and I don't think that's right. 

I must be putting something in the wrong place but I just can't see anywhere else I can allocate it without knocking out the other forms AGI.