I've been using gedit to compose my long posts in my Linkshell Community, using its character-counting tools to keep me under the thousand-character limit in my postings, and I find that I've been getting the "post is too long" error message even when gedit says I've got 995 or so.
The best I can figure right now is that multiple carriage returns (e.g. between paragraphs) are counted in odd ways.