examine the code.
Note that currently we attempt to maintain a 'flyweight' cache of objects which
we don't hold persistent refs to, and rely on gobject weak refs which notify us
on destroy.  There are two problems - for one, because we call a lot of
gtktreeview/gtktreemodel api and emit signals while manipulating our cache of
flyweight references, it's very easy for objects in our list to die while we're
messing with them or traversing the list.  Even if we keep track of a flag in
the cell_info indicating that a cell has died, we may continue to operate on a
cell (AtkObject instance) in the destroy handler, which can result in calling
atk_object API on an object which has been unreffed already; this is unsafe and
in fact even the basic GType macros can fail when called on destroyed GObject
references.

Obviously architectural changes are required.