In summary, if you have a proper name in all-caps anywhere in any of your contact databases, IOS texting will try and make it all-caps.
I've had this problem as well. Here was my solution for the IOS texting app changing proper names to all-caps.
I figured it out after IOS consistently turned the name "Russell" to all-caps. Of course, Russell can typically be both a first name and a last name.
Between my work and personal contacts, the contact database on my phone has over 10,500 names.
On my personal contact list, I had three instances of "Russell". All were not all-caps.
But on my work contact list (from an Exchange Server), I had 27 instances of Russell. One, and only one, contact was all-caps "DAN RUSSELL".
After correcting the name on the Exchange Server to normal upper and lower case characters, I checked to ensure that my phone had the updated contact. Then I sent a text that included the name Russell. IOS no longer tried to make it "RUSSELL".
Thanks for the hints from everyone on this thread.
Ed in Orlando