You should report this issue to the game developer.
I have the same issue on Mint 14 with 2 monitors. If I have my secondary monitor located to the left in the display settings it will lock my mouse to the secondary monitor instead of the primary one (where bastion starts) However, everything works fine if I move my secondary monitor to the right of my primary in the display settings. It also works fine if I change it to windowed mode in game, but the -windowed and -noborder flags seem to do nothing when I add them in steam, so I'm stuck with a border if I do that.
The fullscreen support in Bastion is handled entirely by the window manager.. Bastion simply request the window manager make it fullscreen. I would suggest swapping window managers to see if that alleviates the issue.. if it does, file a bug with your window manager.. if it doesn't please provide details on which window manager you are using.
I my self am using either Xfwm and am toying with Compiz 0.8.8 and my secondary monitor is to the LEFT of my primary and bastion correctly locks my mouse to the right (primary) monitor where it appears.
This should probably be closed. I'm unable to reproduce this and this is more of a third party issue.
Nothing extracted yet.
(Works fine on the same setup in Windows 8.)
I have three monitors: 1, 3 and 2 (in that physical orientation as well). The game starts up on monitor 3 (correct), but the cursor is locked to monitor 1. I do no have this issue with other games on Linux. Keyboard works fine in the menu, but not while playing the game (I don't remember if you use the keyboard while playing or not, so this might not be a bug).
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