I haven't figured out a real solution, but I did find a workaround - I used this code in site.ini.append.php to just change the redirect from the logout link to a static logout page.
Thanks, Paul, but the problem doesn't seem to be caching. I turned off my viewcaching (templatecaching was already disabled) and it made no difference. I also tried the cache-block line of code, just in case, and it didn't make any difference either. Any other ideas? -looks hopeful-