Thunderbird finding mispelled words that don't exist???

I have a strange problem with Thunderbird spell checker. It is finding
mispelled words that are not even in the email I have composed! There
are things such as mso normal, mso hyperlink, etc. Generally there are
about 15 words that it finds and I just keep clicking ignore until it's
done. I thought about just adding them to the dictionary, but thought
that's just fixing the symptom, not the problem.

Any idea why this is doing this and more importantly how do I correct
it? Thanks in advance.

DanZ