See this question about "Problem Signatures".
Of course this also applies to other reserved words.
Well, currently, it can't.
It's not really a "reserved word" in the traditional sense—there are no technical limitations on using that word in your question title. Rather, there's a word filter in place that intentionally blocks this.
I and several others think that the filter is a bit overzealous and unnecessary. Rather than deterring people from writing bad titles (which it was theorized the word "problem" is a hallmark of), it has just forced people to come up with even less stellar "workarounds", like the one you point to. Many a times, I have tried to edit a post and fix spelling mistakes, only to be told by the system that I actually can't spell the word "porblem" correctly. Somewhat self-defeating, I think.