This is general issue as most recruits put a thank you out to the University of XXXXXX, whether it is correct or not. I have seen University of Tulane, I have seen University of Oklahoma (which is technically correct, but their brand is OU, not UoO), University of Auburn and finally the University of Florida State.
Yes, it is an annoyance, but the truth of the matter is they don't care about a university's branding when they tweet, they care about saying look at me and what I got.