Proposed resolution:

This wording is relative to N4861.

1. Modify [ios.base.cons] as indicated:

   [Drafting note: Wording modeled on container requirements]

   ~ios_base();
   

   -2- Effects: Calls each registered callback pair (fn, idx) ([ios.base.callback]) as (*fn)(erase_event, *this, idx) at such time that any ios_base member function called from within fn has well-defined results. Then, any memory obtained is deallocated.