[Plugin: Google XML Sitemaps with Multisite support] https works and https not

I am not quite sure what I am experiencing here.
I installed the plugin version 4.0.2 and I did NOT network activate.
Instead I activated for one site, ‘example.com’.
I also created a sitemaps directory in the wordpress root and made it writable. The files are created.

My wp multisite runs the admin over SSL, so https://example.com/wp-admin

The ‘detected URL’ is https://example.com/sitemaps/https:–example-com.xml but Google Webmaster Tools doesn’t want to see it (maybe because the certificate is self-signed?). When entered in the browser, it looks fine though.

I changed to manual URL generation, and entered http://example.com/sitemaps/example-com.xml

I checked this in the browser (FF) and got this:

Error loading stylesheet: An unknown error has occurred (805303f4)
https://example.com/wp-content/plugins/google-xml-sitemaps-with-multisite-support/sitemap.xsl

But the sitemap was automatically submitted to Google and it was detected without error.

My guess: while generating the sitemap, the URL of the stylesheet is still marked as https even though the manual URL says http.

So, it works, even while in the browser it doesn’t seem to work.

http://ww.wp.xz.cn/extend/plugins/google-xml-sitemaps-with-multisite-support/