Post by Email: [publicize] not registering

Recently, using `[publicize]` stopped working when used in an e-mail.

Steps to reproduce:
1. Setup a JP site with PBE with Publicize connections enabled.
2. Send an e-mail to the PBE address containing `[publicize off]`

Expected:
Post published, but no social media messages are sent out.

Actual:
Post published and social media messages sent.

The shortcode appears to still work as expected on wp.com, so limited to Jetpack. Reported as failing near June 20th.

2779660-t

Reproduce this on a Japanese WordPress site with Post by Email and Publicize connections enabled, using an email containing [publicize off]. Compare Jetpack's handling with the reported wp.com behavior; done means the post is published without sending social media messages.

Written by the indexing model from the issue text.