An ambiguous string was localized to Spanish in an incorrect way. Selection mode "Block selection" (both in menu and status bar) was translated as "Bloquear selección" (i.e. Lock selection), but something like "Selección por bloque" or "Selección de bloque" should be used instead. PS: I'm using this bug report to suggest a better translation, as I could not find any option to use Pootle without creating a user.
Thanks for reporting this bug, Lucas. I have just made the correction, and it should be available in the next LibreOffice 3.6.x release.