Can anyone recommend a fix for this in Linux? It's basically unplayable without it...

Having this exact same issue in the Linux version of the game. It's essentially unplayable without a hack to lock the mouse to the window and/or the screen depending on which mode I want to play in. I can't even click around in the menu when it's in fullscreen mode, needing to use the keyboard instead. Let me know if there's any info I can give to fix this because it still needs fixing.