Context popup menu far from the mouse
When you select downward text that comprises multiple lines, the Y coordinate of the context menu is at the beginning of the selection. The X is correct.
@molily's component doesn't suffer from this problem (demo).

Fixed in my fork of SelectionMenu that addresses a few other issues from selection-sharer and makes it general (i.e you can put anything you want in the menu).
@dandv can you submit a pull request so that everybody can benefit from it? Thanks!
@xdamman: in the meantime our fork evolved quite radically by using HubSpot's Drop library (which prevents #20 in selection-sharer).
Perhaps it's best we continue efforts in that direction?
I think it is smarter to show the menu directly where the mouse was released.
Change line 148
var top = topOffset + self.getPosition().y - self.$popover.height();
to:
var top = e.pageY - self.$popover.height() - 10;