Why Does Update with No Args Move Bookmark?

[Jensen, Aaron]

> > Why does `hg update` without arguments move a bookmark [1]?  It seems like 
> > this could cause unintentional problems if someone does work on a bookmark, 
> > and un-mindfully runs `hg up`.  This feels like a bug.

> The short answer is that it simplifies the common scenario where you pull 
> changes from some public server, and you have not made any commits of your 
> own. "hg up" moves you to the tip of the current branch and drags the bookmark 
> with it so you are ready to start working.

I agree that pulling from a public server is a common scenario, but disagree that the bookmark should move.  I think the only operation that should cause a bookmark to move is a commit, or a specific command to do so.

Whenever I create a branch, Mercurial warns me: "branches are permanent and global, did you want a bookmark?" If bookmarks are supposed to be lightweight branches, moving a bookmark on an update breaks that model.  If I run `hg up` without any arguments, if I'm on a line that has a bookmark, it should update to or keep me on the bookmark, not to some other line.  Moving the bookmark breaks the branch-iness of the bookmark. This behavior makes it really unlikely (as others have attested) that I'll ever use this feature. And I really, really want to use this feature.