I have just purchased the same radio for the same reason! I don't have a minidisc yet, but I was thinking of getting a Sony Hi-MD model. I have tried one, the MZ-NH700, in a shop and found exactly the same problem you describe when operating from the battery. What I don't know is whether it behaves the same when operating from the mains adaptor, but the manual implies that it does. Like you, I couldn't believe this design 'feature'. Looks like I will have to resort to a non-Sony MD and therefore no Hi-MD mode. What a pity! Have you tried yours on the mains adaptor?
