Drag and Drop to move contacts between address books doesn't work in 52.9.1. Is there a workaround?

Actually, it hasn't worked for a long time. Now, I'm getting a persistent error, "One or more of your mailings lists are broken." I deleted all the contacts in "Personal Address Book," then imported contacts from a backup of the Personal Address Book. Now, I have 2 "Personal Address Book" listings in TBird Address book, only one of which is the "real" one that Thunderbird wants to use. Tried to copy all the contacts from one to the other, then the errors started coming. So, how do I do this -- restore contacts TO the Personal Address Book? AND, why doesn't drag and drop work? There is no other way to copy/paste contacts between books!