I started using the dedicated HOME and END keys after reading about them in a dev reply to eobet's suggestion about toggling between units. Their response is definitely erratic, and I suspect that the instability might be related to running in window mode and switching back and forth between the game and other stuff.
In some games, both HOME and END have simply stopped working or refused to include a particular unit in the toggling list. In my current game I've switched back and forth several times and now the HOME key gets stuck on the no-unit-selected/mini-summary display. That non-unit info display is also 'in the list' for the END key, but somehow doesn't get stuck they way the HOME key does.