You need to retain an experienced criminal defense attorney in Maryland. I think that your Pa record will be used against you, but the Maryland attorney is the best one to answer that question.
A agree with Attorney Keller. A Maryland attorney will be able to answer the question of whether your PA Retail Theft record will be used to enhance the grading of the offense there. I would expect it to have that impact; certainly if the states were reversed in your question the answer would be a definite yes. You don't indicate why your most recent PA case was graded as a Felony, but that is most commonly due to having two or more priors. Accordingly, without knowing the full extent of your criminal history it's difficult to predict a likely outcome on the probation violation here. Without more, my guess is that you have a good chance of jail as a consequence of the violation from MD with yet another Retail Theft. You should repost this question with the area of MD where the offense is pending to get their input. It would also seem to me that you have an underlying problem that needs to be addressed. Good luck.
If your asking because Maryland has a similar statute to Pa where the grading is enhanced for retail thefts based on the number of prior offenses, your question is best served by asking a Maryland attorney. The only thing I can add is that I have successfully argued that out of state prior retail thefts do not count to enhance the grading for retail offense committed here in pa. For instance if you have two prior retail thefts from N.J. then get a new offense in Pa. it will be counted as a first retail theft for grading purposes in Pa. I don't know how Maryland statute is written.