I think I'm a pretty decent senior network engineer but I've been hit by firmware bugs more than once. No matter how much redundancy you build in, there's always shit that can go wrong and there will always be things that you just can't foresee (like the bug in this case). The software on these network devices and optical gear is written by humans, like all software, and is not perfect, like all software.

(In one case I experienced, the vendor reassured me that what I reported was not even technically possible -- until one of their engineers flew out and witnessed it firsthand.)