DashContainer nested menus are incorrectly positioned

[TomTirapani]

If you use groups for your DashViewSpecs they are grouped in the context menu into submenus. The second level of menus are incorrectly positioned - they seems to also open in the same position, rather than anchored to the prior menu item. This can make it impossible to select an item if the two menus do not align properly.

Note that this is not an issue with other forms of nested menus (e.g. grid context menus), which appear to be positioned correctly:

[TomTirapani]

I have set up a Toolbox branch which demonstrates the issue: https://github.com/xh/toolbox/tree/dashContainerMenuBug