Still seeing this with 2.5.1 in Unity 3.5.7f6.
Creating fonts in a new scene does seem to help; in my primary gameplay scene I created two fonts successfully and then kept crashing on the third one (i.e. quit, reopen, try the same thing, crash again, wash, rinse, repeat). In a new scene, I was able to create the remainder of my fonts without issue.
It crashed the first time in 2.3.6, so I checked for a new version, updated to 2.5.1 and still got the crash (this was all in my main gameplay scene). So nothing between 2.3.6 and 2.5.1 seems to have affected it. The crash is still lurking. I reported the crashes through the automated bug reporter.