[wilful]

I think that people are being too quick to assume that user error is the end of the cause of the failures. I have yet to see someone ask why this user error is occurring.

After pondering this, it does seem to be a design flaw. Likely this design flaw is in the documentation and the lack of safety knowledge. If there is a danger caused by stress from over-tightening the threaded fittings, there should be a sticker around the fitting that warns against over-tightening. The same should be true for any other safety issue with any device.

Also for any COTS device, read the manual before use. While the device may not pose an imitate safety hazard from a user failing to read the manual, reading the manual for the product will increase safety while using the product and prolong the life of the product.