A Cross-billed Black and White Warbler

I know I just posted a Black and White Warbler a few days ago, but this one warrants another post. You may want to click on the pictures to see a larger image.

This Black and White has a crossed bill! How did that happen. All markings are normal, so this doesn't seem to be a hybrid. Nevertheless, its bill is crossed.

I am guessing the lower beak must have gotten broken some time ago and the upper beak grew down crookedly. Yet, in the second picture, the lower bill seems to be just as long as the upper bill.

Now, how does this aberration affect its ability to catch flies?  He must have adapted successfully, because he looks healthy. Even the most common bird can be uncommon:-)