Best summarized as:
"Major @googlevoice fail today. Eight texts from me to my wife came from eight different phone numbers."
https://twitter.com/travispew/status/265858873498402816<p>Ongoing support thread:
https://productforums.google.com/d/topic/voice/OUmPhUpujjs/discussion
This is the intended behavior. They piggy back off of a large group of local numbers. For texts they assign one to you for a short period then put it back in the pool.