I have a Macbook Pro with a 23" Apple display connected as a secondary monitor.
Normal Behavior: Entering Full Screen Mode with on the primary display I can pull up the Control Panel by moving the mouse to the bottom of the primary display screen. No problem.
Strange Behavior: Entering Full Screen Mode on the secondary display causes the Control Panel to appear for a few seconds and then reduce like normal but then it never comes back no matter where I put my cursor long the bottom of the secondary screen.
Work Around: I can get the Control Panel to come back on the secondary display if I move the cursor very quickly form the White Page Docment area to the bottom of the screen. But if I let the mouse cursor linger too long in the small gap between the bottom of the Document Page and the bottom of the screen then the Control Panel will not appear. Likewise, the Control Panel will not appear if I approach the bottom of the screen from the darkened area outside the Document Page.
This bug pertains only to whichever is the secondary monitor. If I swap the displays so the 23" monitor is primary and the MBP display is secondary then I get the bug on the MBP display but not the monitor.
I see that another poster had a similar but not identical problem about 9 months ago but the forum thread does not indicate a fix. See thread here: https://forum.literatureandlatte.com/t/lost-my-full-screen-control-panel/2268/1
On another note, I agree whit this person: https://forum.literatureandlatte.com/t/full-screen-control-panel-transparency-awesome/104/1 full screen + transparency (+ typewriter scrolling) = awesome!