PA royalty income

[Gail in Virginia]

I have a client, Virginia resident all year, who received a 1099MISC showing royalty income with PA tax withheld.  They had a 1099 for the same place last year, but no tax was withheld.  The amount went from less than $1500 to $1886 this year.  The income is listed as being PA income this year.   Last year it did not indicate a state but I am sure it was the same.  If I fill out the PA non-resident taxes, they owe $4 more than was withheld even though this was their only PA income.  But I hesitate to mark the box "not taxable on Schedule E in Pennsylvania" without know why it would or would not be taxable there.  Any PA preparers (or smarter than me people) who have any advice?