67.0.3383.0 (Official Build) dev (64-bit)
Google_Samus.6300.276.0
Chrome OS with flag enabled: #enable-experimental-accessibility-features (not needed for this repro, this is on because I found this during testing another feature)

# Enable ChromeVox
# Launch a Google Sheet and have a few cells highlighted
# Go to mail.google.com and put focus on an email in the inbox
# Let ChromeVox read the preview info for the email, it then starts reading the contents of the Sheet in another tab.  

I wasn't able to reproduce this after several attempts. Therefore, I am opening and closing this bug just in case I can repro this in the future.