RewriteRule causes page to reload twice

I shaped two different RewriteRules for my page:

# Enable URL Rewriting
RewriteEngine on

# exclude followed stuff
RewriteRule ^(js|img|css|favicon\.ico|image\.php|anprobe|content|libs|flash\.php|securimage)/ - [L,QSA,S=2]

# conditions (REQUEST dont point @ file|dir|link)
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-F
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-l

# rules
RewriteRule ^(?!index\.php)brillen/(.*(brillen)|360|neu)/(.*)([a-zA-Z0-9]{5}-[a-zA-Z0-9]{5}(?!\.))(.*)$     /index.php/brillen/$1?art_id=$4&$5&%{QUERY_STRING}      [NS,QSA,L]
RewriteRule ^(?!index\.php)(.*)$                                                            /index.php/$1                                   [NS,QSA,L]

... and I'm encountering a strange problem, which lies in every request causing the page internally to load twice, which leads to the problem that db actions and email dispatching are also executed twice.

Does anyone have an idea concerning that?

Thanks in advance!

Note 1: All requested resources are valid and available according to the browser's resource tracking.

Note 2: May the problem originate in retaining and post-processing the PATH_INFO? (/index.php/$1 => /index.php/foo/bar/...)