Starting with 1.8.2-pre5, the game sets my monitor resolution to 960x1200 when exiting. This is exactly half its native 1920x1200 in the x-direction. I have a dual-monitor setup:

Primary: 1920x1200
Secondary: 1920x1080 (right of primary)

Steps:
1. Select version 1.8.2-pre6 in the launcher.
2. Start the game on the primary monitor.
3. At the main menu, quit the game. At no point do I enter fullscreen mode or even attempt to resize the window.
4. Both monitors briefly flash. Primary monitor is now at 960x1200 according to its on-screen display; secondary is still at 1920x1080.

To fix the resolution, simply starting 1.8.2-pre4 or earlier and quitting resets it back to 1920x1200.

For the benefit of other players running into this, a more convenient fix involves the xrandr command. The commands are (the --output names will vary, use xrandr -q for a list)

xrandr --auto --output DVI-I-2 --mode 1920x1200
xrandr --auto --output DVI-I-3 --mode 1920x1080 --right-of DVI-I-2