.htaccess file being modified

On one of my WordPress installations, there appears to be a random variable that alters the syntax of the .htaccess file. When it first started, it would look like this:

# BEGIN WordPress

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

and be modified to look like this:

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

# END WordPress

My server support believed this issue could be caused by either one or a combination of installed plugins. On the most recent reoccurrence they identified that the file had been modified when wp-cron.php was run (whenever a visitor came to the site). I tried to disable this, but the site went down again when the admin user tried to make a change to the site. The file now looks like this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{RERewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ RewritRewriteCond %{REQUEST_FILENAME} !-f
# END WordPress
QUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

When it should look like the above example. Has anyone got any idea what the hell could be causing this and how to resolve short of re-installing?