Imagine this:

1. A friend sends 30 people an email saying "Hey, BBQ at my place this weekend?".
2. You open it up in gmail and click in the reply box.
3. The full reply window displays itself you and you write your response: "Can't go this weekend - we have a wedding to go to."
4. Hit send.

Until a couple of weeks ago, this email response would just go to your friend. If you wanted it to go to everyone, you would have to hit "Reply to all" and it would automatically CC everyone.

For some reason, gmail changed this, and it now defaults to "Reply to all". (This can be verified by playing with the "Older version" in gmail)

What's the problem? The problem is that when I accidentally discovered this, I let my friend know that Sara and I were engaged - something I hadn't let anyone else on the email list know. Is it a big deal? No. But it wasn't really how I was planning on letting them know.

I consider clicking the text entry box at the bottom of an email a shortcut, and arbitrarily changing shortcuts in programs to do almost-the-same-thing is very bad.

On the other hand - this is probably the way gmail should have been working from the beginning. The problem is that users get used to one behavior - and if that behavior changes, it should be made VERY clear.

It could have been a lot more embarrassing.