Accidental ~ Safety from testing...
The replacement of the check valves by burst disks, which seal completely until opened by high pressure are a once only use solution but then the need to fire the SuperDraco thrusters, that are hopefully never needed, are to save the crew capsule, in the event that there is a failure of the launch vehicle.
The use of check valves was because SpaceX was conducting multiple static fire engine tests, that the abort system does not require as the SuperDracos are designed to push the spacecraft away from a failing Falcon 9 and are only to be used in the event of a launch escape scenario.
So we now have a much safer Crew Dragon capsule as the result of this fortunate unplanned disassembly of a Crew Dragon capsule and a system design, that should in retrospect of been used in the first place!!!
Titanium is a metal that given the opportunity combines readily with many elements but I wander was it the titanium, or another substance in the check valve or plumbing, that reacted with the nitrogen tetroxide with such violence!!!