I've interviewed several great senior engineer candidates over the last few years, and then had to watch do this and walk themselves right out the door inside of 6 months. I've developed a marked preference for promoting internally, because you get longer to head this sort of thing off.
Incidentally, this sort of thing is why software engineering desperately needs some sort of formal levelling criteria and/or mentorship programs. It's really hard for senior folks to calibrate themselves against their rapidly shrinking peer group.