Mail right preview pane error

Hello,
Since SL I have an annoying issue in Mail . I liked the right preview pane in Outlook and it was great whenit his feature was added in snow leopard.
When replying or forwarding a message using the grey icons in the preview pane it opens two reply or forward emails.
The issue is the same in Mountain Lion email.
Thanks

Are you by chance double-clicking those icons? That's the only way I could reproduce what you report on my machine.