(I'm not sure I'm right on this meta site, but since there's a bug tag...)

The following is a link to a web page with a trailing ) in its URL:

test

I know, the parentheses can be escaped, but that's not the issue here.

It's markdown live preview looks like this (apart from the actual URL):

test)

I.e. the trailing ) of the URL is thought of as the close parenthesis of the markdown code.

Now, if everything goes as I remember, the finished post will have a link that looks like this:

test

Therefore, the server-side markdown parser behavior is different from the JS live preview.