No problem. I've seen that error more than a few times and it was nice to finally be able to replicate it.
I did find that thread and the OP had moved the Profile button. Which resulted in the same error just for a different button this time. Basically that error will occur any time there's a $_GET['action'] and no corresponding button.
So I guess it can be considered to be a bug.
I think that both topics could be related to this. For the second, members report the buttons disappearing at times.
But for the first link, that scenario should covered. Unless the search button is missing.