re: Is this normal?

It's not that odd for some manufactures to request that a product that has been "warranted" to be destroyed. This is pretty common practice in the appliance industry because of the liability of the old "defctive" product. Generaly, there are agreements between the manufacturer and the distributor that binds the distributor to destroy/make inoperable any warranted gear that they receive back. I dont think that I've ever seen a manufacturer request that of a end user but most of my experience is with wholesale or large retailers that require that gear be returned to the point of distribution for warranty replacement.

So, with all of that bing said...I don't think that it is that odd of a request that they are aking you to provide evidence that it has been put out of commission. But like I said before, if a manufacturer is worried about liability, they normally leave that task to be done by the distributor and not Joe Homeowner.