1. I don't know. It could be some browser setting or it could be some setting at certain sites. It might also be a particular editing mode you are using. Or it could be some invisible characters sneaking in.

2. I'm not sure about "linkify" or "clickify," but the intent seems obvious, so you shouldn't hesitate to use them, if there is no better word. "Clickable" is a very common usage. We used to use the word "Hyperlink" as both a noun and a verb. So "I will hyperlink that." One could say "Hyperlink a URL," but it may be ambiguous.

3. A URL is more than an "address," although some of the information may be implicit. The address is derivable from the URL. The URL specifies a protocol (http, telnet, etc) and can contain other stuff (like port numbers, user names, passwords). The wordsmith.org is not the "address."