php - Website returns error 404 with content -

i switched new webhosting , found unusual error - pages except root on website returning 404 error, actual html of page.

as example, can give page:

http://www.mm-vet.cz/cenik 

it returns 404 error actual page html(so can see in browser).

here .htaccess

rewriteengine on rewritebase / rewriterule \.(css|jpe?g|gif|png|js|ico)$ - [l] rewritecond %{query_string} !^cat rewriterule ^(.+?)/?$ /index.php?cat=$1 [l] 

why server returning 404 error when page exists , how can fix it?

is there specific reason why targeting set of extensions? can work using simpler rule check whether requested file exists and, if not, performs rewrite?

rewriteengine on rewritebase / rewritecond %{request_uri} !-f rewriterule ^(.+?)/?$ /index.php?cat=$1 [l,qsa] 

does php code, @ point, send header('http/1.0 404 not found')? being invoked?

i have never experienced webhost sending 404 errors, sending requested content.