In VisualEditor, it is not always possible to save a paragraph that ends with <ref>(cite source)</ref>。 Upon saving the page, the full stop disappears. See the original report.
I successfully added one in my sandbox at MediaWiki, but (a) I pasted the Chinese full stop into the text, rather than entering it normally, and (b) when I pasted it after the ref, it gave me a black sun before the full stop. Also, I'm running Safari on a Mac, so it may be browser or OS dependent.