If you specify a width for a CCLabelBMFont, in the previous versions of cocos2d it would break overly long lines at word boundaries, but v3.4 breaks them anywhere, thus inserting linebreaks within words, which breaks it quite badly. Is this a bug?
The code in CCLabelBMFont that inserts the linebreaks seems identical compared to the previous version, so the problem seems to be somewhere else.
Edit: Oops, I was comparing the wrong versions. There actually are some changes in the implementation of CCLabelBMFont in v3.4 compared to 3.3. Something probably broke it.