The first time this happened (several days ago), I joined a server, the server admin started the game, and it was when the game loaded I saw the cursor was missing.
Second time (today), I quit a 4v4 game (we were losing

), and after clicking the exit button to leave the stats page for that game, my cursor once again had disappeared.
I've not been able to retrieve the cursor without restarting the game. Sadly no error reports popped up when this happened. It appears to occur when transitioning from the menu-to-the-game, or vice versa.