Comment 8 for bug 852458

The problem is that aptdaemon invokes dpkg three times, as mentioned in the dpkg manual
http://manpages.ubuntu.com/manpages/trusty/man1/dpkg.1.html
"Note: front-ends might call dpkg several times per invocation, which might run the hooks more times than expected."

My very ugly workaround is to check if any snapshot has been made within the last 60 seconds. I'm attaching my modified /etc/apt/apt.conf.d/80-btrfs-snapshot