Previously sent image pops up in preview when trying to see an image just sent.

A friend of mine sent me a picture via iMessages. I double-clicked it to make it bigger and but an image she'd previously sent me popped up instead. Any ideas as to why that would happen?

This is what it looked like when she sent it:

And then when I double clicked that image, an image she'd previously sent me popped up:

You can see that the image she just sent me is highlighted as it's got that grey over it and yet that other image pops up. Odd. And this happens a lot. Any ideas?

Thanks!

- Leigh