Issue with resize events when closing multiple Notebook ListEditor tabs under Qt

Observed in code that I can't reproduce here: when closing multiple tabs at the same time (eg. when replacing the entire list) with certain editors, we get crashes.

What we think we are observing is that there is a race condition happening where the first item being deleted generates a resize query (possibly from a new tab being displayed) but the object has been deleted before the resize query is generated.