When you play on an external monitor and have your built-in laptop screen disabled, xrandr's output is as follows (LVDS-1-0 being the built-in laptop screen):

Screen 0: minimum 8 x 8, current 1920 x 1200, maximum 16384 x 16384
LVDS-1-0 connected
1366x768 60.01 +
1360x768 59.80 59.96
1024x768 60.04 60.00
960x720 60.00
928x696 60.05
896x672 60.01
960x600 60.00
960x540 59.99
800x600 60.00 60.32 56.25
840x525 60.01 59.88
800x512 60.17
700x525 59.98
640x512 60.02
720x450 59.89
640x480 60.00 59.94
680x384 59.80 59.96
576x432 60.06
512x384 60.00
400x300 60.32 56.34
320x240 60.05
VGA-1-0 disconnected
HDMI-1-0 connected primary 1920x1200+0+0 495mm x 309mm
1920x1200 59.94*+
1600x1200 60.00
1280x1024 60.02
1280x960 60.00
1024x768 60.00
800x600 60.32
640x480 60.00
720x400 70.08
DisplayPort-1-0 disconnected

Having a monitor that is connected but disabled trips up LWJGL, which in turn crashes Minecraft.

If I hack the output sent to LWJGL so that LVDS-1-0 is shown as disconnected, the game works correctly.
Minecraft 1.8.1 and prior versions are not affected, and neither are other games that use XRandR.
This bugs makes MC 1.8.2 and higher versions unplayable on any Linux system with connected and disabled outputs.