Why don't captions match images in photomail?

Thanks for getting back with me.

Below is one image out of a gallery of 17 that I sent out recently. The image is correctly captioned “northern parula”.

However, a recipient says this is what she sees: The caption is still there, but an image of one of the other photos in the gallery is displayed. In this case, the bird shown is an American redstart not a parula.

Doing some experimenting, I thought we had identified the problem was caused by me sending too many images in one gallery, in this case 17. I sent out galleries of 8 and 15 images to a number of people and all reported the captions matched the image.

So I sent another 8-image gallery out. Most people said it came through perfect, but one recipient reported the problem below.

I sent this photo of a tiger swallowtail – correctly IDd on my retained sent email.

But a recipient sent this back to me. Not only does the caption not match the photo of the red-headed woodpecker, but that image was not even in the gallery I sent. In fact, it is not in my current PSE catalogue. It is in my folders where I keep my Nature photos. So somehow, PSE has managed to retrieve either the image from an old catalogue or from my folders, sent that image to a recipient and yet, my original email does not show this image to be a part of the transmission.

Hope you can help.