It's driving me nuts too...
I apologize for the screwy font size changes that occur sporadically throughout my posts. I think the problem starts when I excerpt more than one paragraph from another source. Despite my best efforts to date, I cannot resolve this - but I'm not giving up.
Worst of all, it doesn't show up on my preview screen.
Of course one obvious work-around would be to limit my excerpting to single paragraphs, but that means more work for me. Seriously it also limits the context for the point I'm trying to highlight.
Anyhoo, we are beefing up the AgWeb section of FJ media, so I hope to have some professional help soon.
Meanwhile, thanks for your consideration.