This has been initially reported at https://ro.wikipedia.org/wiki/Wikipedia:Cafenea#Problema and I was able to reproduce it.
Go to any Wikipedia webpage and click the edit link. Expand the special characters section and click on any of the buttons there. On the first click, nothing happens except some kind of scrolling of the page. On subsequent clicks, the char is correctly in the edit box.
Apparently it works in older versions. User agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
Version: unspecified
Severity: normal