Chrome Version: 57.0.2987.6 (Official Build) dev (64-bit)
OS: ChromeOS

What steps will reproduce the problem?
(1) Set up two monitors on Panther, left on DisplayPort, right on HDMI.
(2) Configure the right monitor as "primary".
(3) Install ChromeOS M57 update.

What is the expected result?

Expect that monitor configuration is unchanged.

What happens instead?

Left monitor (DisplayPort) is now the primary monitor.

It is straightforward to re-set things back to the way they were, but unexpected that an OS update would change settings.