There isn't a fix (as far as I've seen) and it only affects a small number of phones, so I doubt it'll get any attention (at least for a while)
It's not a network issue, can't be. It's gotta be software based, and seeing as how it happens with 3rd party messaging apps too, I assume it has to be a problem with the phone book software.
Our phones are some of the first to store the phone book in the cloud (all your contacts are "google contacts" saved to the google server.) With the exception of contacts transferred from old phones, which is saved in a text file on the phone. An interesting fact that I just realized is that all the contacts involved (either incoming message assigned to the wrong contact, or outgoing to the wrong contact) are stored in the cloud. At least that's my experience.
With that being said, the problem has to be within the relaying of information between the phone and google, loosely making it a network issue, but primarily being an issue with the software. I don't know if that lands on the shoulders of Motorolla or google. Anyone know who wrote the included apps for the phone? Does the G1 or HTC droid use the same phonebook app?