CSST bonding

Could you please send me anything that you have that would explain the need to have CSST bonded? I am in the process of arguing with a builder who says that because of the vinyl coating on the CSST it does not need to be bonded. That goes against what I always understood from you. This is on my listing in Waukesha (only 3 years old) that had the CSST called out on the buyer's report. The seller's builder is saying that it's not necessary. I thought I had a good explanation of why this isn't up to par, but I can't find it.