Motorola A855 only receives one MMS per thread?

I have a non rooted Motorola A855, and last night, my girlfriend sent me MMS of her brothers who are up for Christmas. This morning, she tried to send me a picture of her laptop, but I didn't get anything. As in, nothing. There was no prompt, no indication of any kind of second message sent. I had my friend on the AT&T network send me two images, and I only received the first. Again, the was no indication of a second image.

My mom's phone is on Verizon (as am I) and was able to send me two pictures in succession.

Is this a carrier thing? Can I workaround this? It's really kind of annoying and it's my only complaint about this phone. Everything else is amazing on it.

EDIT: I am using the stock messenger service.