something is writing to my htaccess file

Every so often, started out about once a week – now it is more like every 24 hours – my website goes down (500 internal server error) due to a problem in the .htaccess file. Once I rename the file and allow WordPress to write a new one, everything is just fine.

Finally, today, I decided to investigate this problem further (please excuse my laziness!). The difference between the old (non-functioning) .htaccess file and the new file is simply an “s” at the bottom of the text.

It looks like this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress
s

Yesterday, I updated all my plug-ins and it still happened today. Today, I’ve deactivated all my plug-ins (except for WordPress.com stats & Akismet – although, if you think I should scrap those too, I will) and I’m waiting to see if that works.

In the meantime, any idea what I should be looking for that might cause this simple but disastrous problem?

Here’s my URL: http://www.handmadeinpa.net and it’s running 2.8.6

Thanks!