If you open a document in edit mode and then go back to the view, you can open the same document in edit mode as many times as you like. Notes has had this problem for a long time.
The problem is that it’s impossible to prevent users from conflicting themselves. The client should recognize that the same document is already open for edit in the workspace. In fact NotesUIWorkspace.EditDocument provides this function as an option. It should be the default operating mode of CTRL-E and right-click → Edit.
And because there’s (still) no visibility to the workspace UI elements, I can’t even check programmatically if the document is open.
And if anyone even thinks of asking why users are opening the same document twice I’ll slap you from here to tomorrow while yelling “BECAUSE THEY ARE USERS!!” in your ear.
I’m never going to program in XPages so I’ll never know, but I wonder if a user can do this with an XPage. If the page opens three document, can the user create three save conflicts at one time? Oy…glad I’m never gonna find that one out.