Don't worry... Everytime I applied for a new visa they would stamp same way my old ones... maybe they do it so it is easier for them when they check passport. I think I have 5 visas in my passport hehe... if they were not stamped it would be really hard to find the good one
"Жизнь измеряется не числом вздохов, а числом мест и впечатлений, когда у вас перехватывает дыхание"