Don't send multiple update-cancel messages to an event

Change-Id: Ib64da11ed5584c1a2eef98378d3201a6949fac7d
Closes-Bug: #1376900
(cherry picked from commit 75242b9c67aafa80b4d4a13cfae6c50ba7f85b79)
Merge "Don't send multiple update-cancel messages to an event" into proposed/juno