1. There have been some reports of duplicate posts. I think this happens when you, perhaps accidentally, click the Save button more than once the first time you're saving the post. The reason this is a problem is that there's invisible metadata stored on the "summit" of the post, the line that holds the title. One of the bits of data is the ID of the post. The first time you save there is no ID, that's the cue to the server to create a new post to store the text. If you click it twice, normally that's not a problem -- it just saves the post twice. But could be a problem the first time.
The simplest way to deal with this is to have the button wait until the save is complete. I've been doing it in a separate thread, mostly for esthetic reasons (if I remember correctly). I'll try not doing it in a thread.
It is esthetic, but not trivial. It feels a bit like the software has crashed while its saving. Mostly because you get the rainbow cursor, I guess. But it comes right back. Let's leave it like this for a while and see what happens.
My theory is wrong in every respect. I have a duplicate post myself and I surely didn't hit the Save button too rapidly. I have years of training, and in all that time this has never happened. So the obvious answer is there is a bug in the server side that creates duplicate posts. Or something like that.
2. How to insert a hyperlink. The right-click menu in the outliner offers a way to create a link node. See the OPML 2.0 spec for an idea what that is. That usually isn't what users want -- they want to hot-up a bit of text with an address. That's what the Add Link command in the HTML menu is for. First, put the URL on the clipboard. Then select the text you want to link from. Then choose Add Link from the HTML menu.