Mary,
I made several tests with the BCU version published in BitBucket and with other versions still in development and the they don't show this problem. I even used the word "span" and spanish" to replicate the problem.
Is it possible a Bottstrapbase v2 error only?
Anyway I will report it because the only use of the word span inside the title breaks the site. And this is very common in spanish language academies. So the impact could be high.
Your solution is great and simple and could be the patch for the problem. I will try to apply it asap in all my themes.
Regards
Fernando