Deleting head of a multiple hierarchy causes fatal loop

This can be illustrated quite easily by creating a hierarchy of the form:

2 heads (h1, h2)
1 middle term (m)
2 bottom terms (b1,b2)

It will be displayed as

h1
-m
--b1
--b2
h2
-m
--b1
--b2

If you now try to delete h2, it will warn you that it will delete all the children but actually runs out of memory and fails to bootstrap.