I worked in PA for 4 months and live in Del. TT said I would get $900 from PA but PA Tax Team says I get $0. How did TT get so wrong?

I worked in Pennsylvania for 4 months in 2016, but lived in Delaware.  The other 8 months, I worked at Delaware firms.  During my time working in PA, my employer deducted PA (almost $1200) and DE (over $600) taxes from my paycheck.  I went through TT Home & Business, bought the PA state return and e-filed, and was expecting almost $900 in refund from PA, as that was what TT showed.  However, I received letter from PA Dept of Revenue stating that they adjusted tax return and now my Tax Due/Refund = $0.  How could this be so different from what Turbo Tax PA state said I would receive?