Every once in awhile, the spell checker will get disabled for a document or a portion of a document. To reset it, I usually click on Review | Set Language, then uncheck the Do not check spelling or grammar option. Sometimes this doesn't work and I have to click a language then Default.

In File | Options | Proofing, the first 4 options in both sections are checked and the Hide options are not checked.

Can anyone explain to me why this is happening and how to prevent it from happening?