"Answer to all" option dividing e-mails

I had an e-mail with 6 people on it, as you can see below.

When using “answer to all” option, it does this:

Which is absolutely terrible. If any of this people answer, they need to add everyone on the e-mail once again, and when I answer, everyone is split again.

Hello Guilherme,
it seems that you sent you message as a mass mail instead of one message with multiple recipients.
Wasn’t there any popup window warning you about this?
Did you use the main Send button or Menu>Message>Send as Mass mail option?
Did you use any variables in this message?