Purely out of curiosity, what causes this problem?

As some will be aware, I suffered this problem while attempting to unroot (it kept failing on the radio) so I could send my phone off to repair the rebooting problem I also suffered with.

I'm tempted to re-root but I am reluctant to do so until I'm sure the reboot problem is fixed. However, if/when I needed to unroot and flash a stock ROM, I wouldn't want to encounter this radio brick problem again.

Is it pot luck? Or is there something one can do to avoid it?