Forwarding via a mail rule sends plain text message

My email configuration is such that if I forward an email message manually, using the menu item, the message is sent as expected, in the original message format, including any mages or rich text/HTML formatting. However, today I found that if I used a mail rule to forward a message, it was sent as plain text, so any images and rich text/HTML formatting were lost. This problem has been reported several times in the forums, but apparently has not been resolved.

In my forwarding mail rule I had included some plain text to insert before the original message, which is specified using the "Message..." button of the forwarding rule. I had set it to something like "Forwarded by mail rule." Thinking this plain text could be a culprit, I tried adding some rich text formatting (e.g., making the text red italic), but the entire forwarded message was still sent as plain text. Then I deleted all of this "Message..." text from the rule, and forwarded messages were sent correctly formatted with their images and rich text.

This seems a clear-cut cause and effect, can anyone else verify this? I'm tempted to file a bug report with Apple.