Though the icon seems to be live it makes no difference when I switch it on or off, it doesn’t check the spelling.
Please provide more details (operating system, LibreOffice version, text language(s), installed dictionaries, etc.). — Related questions and answers → Tags, matching “spellcheck”.
I have the same problem. I am using LibreOffice 3.6 on a linux mint v 13 opperating system and the spell check function does not work.