Yes , I'm with 1.8.1. But the thing that must be maximized is not "Game" tab (Play mode is not necessary too).
Instead the thing that trigger it is: maximize a docked PM tab then restore it to docked state. Now changing the active GOs in the hierarchy no longer updates the PM window, same with FSM dropdown (but its still changes the active GO). Looks like in both cases the active object is changing, but PM window is not updating properly.
edit: Sent bug report too.