Timeout Offset by 2 minutes

For testing purposes I set the logout timeout to 180 seconds (with auto refresh set to 1 sec).
However, on login I consistently see the countdown block starting from 00:05:21
Automatic Logout is enforced correctly when display reads 00:02:21
I verified the same behavior with both Firefox and Opera.
With the latter I also see the interstitial warning "You will be..."
I do not see the warning with Firefox.
Javascript Countdown Timer: 5.x-1.21