Sorry to cause such a flap. I figured it out. Sort of. "Operator Error." Experimenting, I attached a random jpg photo to a newly-composed email, and observed the suspect attachment icon with the "remove" (only) statement below it. I went ahead and sent the email to myself to see how it would turn out, and there was the attachment, complete, intact, accessible, and normal.
I've never noticed this happening before, apparently it's been the normal way it works. Once again, I'm closing this issue, and sorry to be a nuisance.