To determine if you file as a resident of MD, review this https://taxes.marylandtaxes.gov/Individual_Taxes/Individual_Tax_Types/Income_Tax/Filing_Information/...
To determine if you file as a resident of PA, review: https://www.revenue.pa.gov/FormsandPublications/FormsforIndividuals/PIT/Documents/rev-611.pdf
If you spent more than 183 days physically in MD , you would need to file a MD resident return. But you indicated that MD is a part time job so probably not total 183 days. If the list of activities cited in the PA pamphlet indicates your residency is PA (especially the voter registration where you declared yourself to be an eligible resident ) thus it appears that you maintain temporary living quarters in MD, then, under the reciprocal agreement between PA and MD:
1. You would file as a PA resident and declare ALL income, regardless of where earned on the PA return and pay PA taxes.
2. Under the reciprocal agreement between MD and PA, MD agrees not to tax the wages of a PA resident. You would file a MD non-resident return requesting a full refund of taxes withheld. And I'd advise you to use only the PA address for official records with any MD employer.
So you would need to file a MD non-resident return to obtain a refund and an amended PA return declaring ALL income.
Yes
No
