Twilio "double dips"

I have Twilio working. BUT when I restore a backup onto my work PC from my development PC I get TWICE the messages sent to my phone when both PCs are running and only 1 set of messages when 1 PC runs.
Am I doing something wrong or is it a “feature”?

Why is this a surprise? Dev machines need to be isolated from anything running for real. Fake everything around them that you need to test.