Interrupting a playbook - interrupt failed to prevent a reboot for ~ 1/2 of hosts in a group

I have a playbook that has a reboot directive at the end, with a pause and prompt at the end to allow me to interrupt and abort the playbook without rebooting. Or at least, it used to.

I pointed the playbook at ~28 machines. Twice yesterday, it rebooted half the machines even though the play had paused and I cancelled it with Ctrl+c and then Shift+a. Each time I ran the playbook, half or more of the hosts proceeded on to the next step and rebooted in spite of the interrupt. When I test on localhost now (only one host), the interrupt works just fine with ‘a’ or ‘A’. Can this be caused by my parallelization being too high for my control host?

ansible version: Ansible 2.1.0

The command line prompt for abort states to use “A” to abort, which is why I used shift+a.

Press ‘C’ to continue the play or ‘A’ to abort

From the docs:

To abort a playbook: press ctrl+c and thena.