I noticed this issue after doing some tests in the Sandbox chat room related to this other bug alert. I was playing around with some weird fake and badly formatted urls until I came out with this one.
Now, you may see that the "FTP" part is getting stripped in the rendering, what you won't notice is that the ":" character after "HTTP" gets stripped too. The actual link result is:
Obviously, if the url was a real one, this would break the link. I still have to find a case of a real url that trigger this bug though, so I don't know if it is worth fixing. Will let you know if I discover something more.
I think that the auto-detect link script is attempting to recognize the second part of the url as an url too, and it stripes the characters, but I'm not sure. Anyway, as you can see, the bug is still present here on the board - see the above links and you will see that the ":" character is lost here too.