Chrome Version: 53.0.2785.4 dev (64-bit)
Chrome OS Version: 8530.6.0 (Official Build) dev-channel cyan
Chrome OS Platform: Acer R11
Network info: N/A

Steps To Reproduce:
(1) Boot.
(2) Log in.
(3) Rotate screen past 180deg.

Expected Result:

Touchscreen UX should activate and keyboard/mousepad should be disabled.

Actual Result:

Touchscreen UX doesn't activate (e.g., onscreen keyboard will not appear when text field clicked) and keyboard remains active.

How frequently does this problem reproduce? (Always, sometimes, hard to
reproduce?)

Always.

What is the impact to the user, and is there a workaround? If so, what is
it?

Tablet mode is unusable; no workaround.