I'm a software developer, and this makes me very angry. The fact that a "magic value" can trigger a bug like this indicates that there is something rotten in the fundamental approach the developers of this particular software took.
There had to be multiple pairs of eyes looking it over, too, and either no one was confident enough to speak up and say "Hey, this isn't the right way to do this", or they were and were then overruled by someone with more authority than sense.
To be clear, I see this kind of thing all the time. I just don't work with safety-critical software, and I had hoped the standards were materially different for that.
I'd love to see the technical explanation of the bug and/or overview of the code, but I suspect it would just make me angrier.
I also quote this post from The Register article's comment page, with which I agree completely:
The bug itself is very troubling, but what is much troubling is what the bug implies about the quality of the software at large. First it implies a lack of bounds checking on the display unit. Second, a lack of testing on the display data inputs. Third, no checking of what the FMS is pushing out. Fourth, no one bothered to write a rational error-handling on the display unit in case values were out-of-bounds (especially since this causes the entire display to go dark instead of just a single value).
But what really worries me is that a software glitch can trigger a failure of all display units simultaneously, rather than just ones showing specific pages. SO would a bad value that is only displayed on one of those tertiary EIS display pages cause the displays to go out as well? What about garbage from the WX Radar?