Sitemap and permalinks problem

I have installed last version of this plugin (1.7.3.3) and I have 2 problems:
1. if I set permalinks to “Post name” when I try to click on “XML Sitemap” the plugin open “http://www.mysite.com/sitemap_index.xml/” and not “http://www.mysite.com/sitemap_index.xml”. If I try to open “http://www.mysite.com/sitemap_index.xml” the browser open “http://www.mysite.com/sitemap_index.xml/” (slash as last char).

2. if I set permalinks to “default” when I try to click on “XML Sitemap” the plugin open “http://www.mysite.com/sitemap_index.xml” (without slash) but I get error 404. I have also try to disabled/enabled the sitemap but I get the same result.

Any idea?
How can I generate the sitemap?
How can I open the sitemap with “Post name” permalinks?

Thanks

https://ww.wp.xz.cn/plugins/wordpress-seo/