There are two issues:

First, when playing the game, it isn't clear how you could get the mouse cursor.  I had to push several keys (starting with "P") to find out that I had to push "Esc" to pause the game.

Second, if the cursor somehow escapes the game, it traps the cursor between two invisible barriers, making it impossible to get to a left-hand side panel (my preference for panel location).  This is especially frustrating if you don't have any idea that the program is running!  And it's especially frustrating if you restart your computer, hoping that the problem will go away, but have it remain.  I was on the verge of re-installing my operating system....

I apologize for not replicating the bug.  I wasn't playing the game:  my daughter was.  I was fortunate that I was barely able to find the issue using Alt-Tab.

Reproducible: Always

Steps to Reproduce:
1.  I'm not sure, exactly.
2.
3.
Actual Results:  
Mouse cursor mysteriously trapped between two invisible vertical barriers that happen to correspond to where the "bouncing tray" can move, if you're lucky enough to find the game...

Expected Results:  
The mouse cursor should only disappear when the game is on-focus; if the came isn't in focus, the cursor should have free range of movement.  Also, it should be clear (perhaps a "note of explanation" somewhere on the screen is in order!  :-) to let players know how to restore cursor movement. 

I chose "Grave" as the severity option, because while there's a relatively easy workaround (find the program, use "Ctrl-Alt-Esc" to kill it--or just use "Esc" to pause it), if you aren't aware of what is happening, and the program re-loads even after a restart (which probably isn't a good behavior for a game!) someone can easily conclude that the only way to fix things is to re-install the entire operating system.

Of course, as much as I HATE restarting my computer, if the game were to be fixed so that it wouldn't re-start after logging out or after re-starting the computer, then that might be acceptable as well.