How do you smell gas for a week and not do something about it? I guess its no worse then the call I found a cracked hx on, the renter asked if that was what had been setting off her carbon monoxide alarm, she then said it was real annoying so she took the batteries out.
the issue is not the flex, but its improper installation!!
a flex is fine when instructions, common sense and codes are followed and the only way to connect a stove, clothes dryer or other moveable appliance. they are also code in some municipalities for earthquake safety.
The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
from an excerpt by Paul Jacob in Sun City, AZ
The OP did not provide adequate information on this but from the pics, it would appear the installer ran gas piping through the return panning, which is not allowed by code, nor is installing a shutoff in a confined space, much less an air duct and certainly flexible appliance connectors are not tested or listed for use in confined unventilated spaces passing unprotected through sheetmetal. Hard to tell from the pics but if the flex was damaged down by the gas combination valve, it could be sucked up into the return where, once ignited down by the valve, could explain the burn pattern.
I agree with Pacnw: instead of vilifying the product, condemn the improper installation and mis-application of the product. Used properly, they have an excellent track record.