Hi folks,
During registering an account for another person in Wikipedia I was able to find the msysterious "Wrong-Captcha"-Bug.
I registered http://de.wikipedia.org/wiki/Benutzer:ChatSocke, see (also timestamp): http://de.wikipedia.org/w/index.php?title=Spezial%3ALogbuch&type=newuser...
At my first attempt the right graphical captcha was "veryours" but it clearly did read as "veryaurs" (which I typed wrongly in and so got the error, although I knew that this was strange English). The little "o" definitely was displayed as a little "a" (the right side was strechted to a sharp vertical line, like in a real "a").
So it is no surprise that en.wikipedians do make less failures on english captchas with undefineable letters.
I hope you can track and maybe solve the problem now (people bug our Wikmedia-OTRS quite often with captcha problems).
Cheers, Arnomane