I have the same issue. I do not see the question "Where is your distribution from?" when I enter the Pick-Up contribution in Box 19. I enter the anount and it does not appear to save. When I go back, the box is blank.
Edit: I may have found an answer. Seems this question has been asked for several years and the issue has not been cleared up in TurboTax. I guess Maryland Form 502SU has to used for the amount to be saved but the instructions are very vague.
MD State Retirement Pickup Contribution
