Goto GMail Open a message that had multiple recipients Reply to it Click "Reply to all" The message content is removed <rdar://problem/5512646> REGRESSION: Changing replies in gmail wipes out your old message
Sent an email to Google engineers and got a response from Michael Davidson, who says that this was fixed recently by Google, and works in an internal build of GMail. He said we can expect it fixed publicly shortly.
This has been fixed.