DeeGee, I run into the problem as well, but apparently far less often than you. I have never "joined" this forum by registering, which could explain the difference. Instead I key my user name and e-mail address every time I post. The only advantages to registering would seem to be the abilities to edit after posting, add pictures, manipulate text, and such. I just don't miss those. The important stuff, such as bold or italic type, adding URLs, and inserting the more obvious smileys, can be done easily enough in one of these posts.
What I do after writing a post is to preview it. It seems that when the spam prevention code changes on the next (preview) screen instead of remaining the same as before, that is when the stupid spam message will appear on the next screen upon hitting "Post message"
even after entering the new code. Not clicking on "Post message" until I get two screens in a row with the same code seems to prevent the anti-spam filter message
most of the time.
If it appears anyway, then I just hit "Back" on my browser, make some minor change, and try again until I get two consecutive screens with the same code. Sounds complicated, but it really isn't. I have never completely lost text in this way, either (though usually I will "copy" just in case). Using the "Back" button always resurrects the screen with the text I entered. Some of you registered users have evidently lost text before, but as a nonregisted user—ironically—I never have.
Hope this helps.