duplicate sitemap

hi, I have installed google image sitemap. it seems to be working perfect. while it was my understanding that it generate a sitemap of images, I see that it lists pages and images. since I already had simple google sitemap plugin, I’m seeing the same pages listed on both sitemaps. I was just wondering if this duplicate was not gonna cause any issues. thank you.
souleye

http://ww.wp.xz.cn/extend/plugins/google-image-sitemap/