Edit as New is usually intended for messages you have sent before, so the From address in the new message is the same as in the original, i.e. yours. When it's applied to a received message, the From address belongs to the original sender, so in most cases TB can't match it with one of your accounts or identities.

Sending a received message to others is usually done as a Forward or redirect.

Thanks for the info but I have been doing this for years without any message. Why now?

I don't know why or when this was introduced, but I suppose it's to warn users when a From address is inserted that might be different than the one intended. There may be a preference that controls its appearance, but I'm not aware of one.