I am an heavy email user. Mail.app is one of the apps I spend the most time with on my Mac and I just found a very serious bug that might compromise information.
Sometimes, I could still not determine a pattern (sorry folks), but it seems to happen when the App is acting slow, you click the Reply All button and the App will open a message editing screen. On this screen you will find the fields To/CC/Subject properly filled, with the detail regarding the message you intended to reply but the Body will contain the content from another random message sitting at your Inbox.
So if you are not careful to check the message thread below you can find yourself replying to people in a completely different thread that has nothing to do with them, thus easily exposing information you wouldn’t want to.
This is a really nasty bug Apple!