Odd that a simple one line fix hasn't made it into any of the official sources.
I'd been using abook for ages (installed via pkgsrc) and noticed sometimes everything bar names and emails would get deleted, but I couldn't track down what triggered it. Fortunately I always had a version I could roll back to. Very recently I tracked it down to adding emails from mutt and I'd started my own pathetic efforts at properly debugging; I'd previously spent fruitless hours (minutes) searching for anyone else experiencing this issue. In frustration at my pathetic attempts to debug I decided to return to searching for existing solutions and finally stumbled across this email thread.
And so that's all I'm doing here: increasing (hopefully) the search base for this issue by linking to it here.