Chrome Version: 57.0.2987.146 (64-bit)
Chrome OS Version: Platform 9202.64.0 (Official Build) stable-channel chell
Chrome OS Platform: HP Chromebook 13

[Please specify Cr-* of the system to which this bug/feature applies (add
the label below).] -- I don't know how to do this.

Steps To Reproduce:
(1) Have multiple users on your Chromebook with both logged in for fast user switching (call them Alice and Bob)
(2) Install the Mosh app https://chrome.google.com/webstore/detail/mosh/ooiklbnjmhbcgemelgfhaeaocllobloj on user Alice
(3) Open a Mosh connection
(4) Switch active user to Bob 

Expected Result:
Do not see the Mosh window in Bob's space

Actual Result:
See the Mosh window in Bob's space

Always reproducible.

This only began happening recently (last week or so?). Not sure if a new version of Chrome, a new version of Mosh triggered it, or neither.

This is mostly cosmetic, could lead to some user confusion around what accounts different windows are in.

I am unsure if this is a bug in Chrome, in Mosh, or in neither.