ipython/ipython — pull request #7046 by ssanderson (2014-11-27 17:56:31+00:00)
Title: BUG: Prevent users from undoing the initial document load with CTRL-Z.

Prior to this change, setting a document's initial content in the text
editor created a history entry, which meant that hitting CTRL-Z
repeatedly could clear the entire document. This change clears document
history after loading so that repeated CTRL-Z applications return the
document to its state at load time.

ping @takluyver