Imagine you have a hierarchy like:

item
  subnode
    subsubnode

Calling "delete all" on the item let the method populate the nodes in the order reflecting the hierarchy in repository (subnode first, subsubnode second). Hence while looping over this collection, we call #executeNode() (aka node.delete()) for subnode first, which is still ok, but once it's about to #executeNode() upon subsubnode it ends up in InvalidItemStateException (attached) because the subsubnode has been removed already by the previous call.

As a workaround one can still do just simple "delete" (hierarchical structure) instead of "delete all".