I apologize. I don't know much about the stability of spritefont, other than that it's definitely unstable when used in certain ways. I think it might have been my first plugin, I was definitely very new to c++. the code was extremely disorganized, and horrifically deformed. And I've also lost said source code, so I can't fix this, and I have no time at the moment to rewrite it. At some point in the future I would like to make a stable spritefont for c1 and c2, but this is not it.
However, there is some good news. minor says he's used it in many games with no problems whatsoever, and he's written a how-to. Try that before giving up. Also, in all my personal tests I had no problem with spritefont. it could be minor's using it the same way I did.