The event CustomTabsCallback::TAB_HIDDEN is always paired with CustomTabsCallback::TAB_SHOWN, except for the case when the screen is switched off (with hardware button).

Application Version (from "Chrome Settings > About Chrome"): 50.0.2661.89
Android Build Number (from "Android Settings > About Phone/Tablet"): LRX22G.T715XXU2APB2
Device: SM-T715

Steps to reproduce: 
Disable device's lock screen (device cannot be locked when screen is turned off)
Launch Chrome Tab
Switch Off the screen with hardware button (mind that the phone doesn't get locked)
Switch On the screen
Leave Chrome Tab

Observed behaviour (order of events (ignoring NAVIGATION_* events)):

TAB_SHOWN
TAB_HIDDEN
TAB_HIDDEN

Expected order of events (ignoring NAVIGATION_* events):

TAB_SHOWN
TAB_HIDDEN
TAB_SHOWN
TAB_HIDDEN

Frequency: 100 out of 100

Additional comments: Also happens when I share from Chrome Tabs as the system's share button is pausing the Chrome Tab's activity