Good point.  In general, if eligibility requirements are met, PA doesn't tax gains on the sale of a principal residence.  I had been thinking that only applies to in state residences, but it looks like they will simply fully exclude the gain on PA Schedule 19 regardless. 

See https://www.revenue.pa.gov/FormsandPublications/PAPersonalIncomeTaxGuide/Documents/PITGuide_NetGains...

Of course, CA will still view it as CA sourced income.