When Smooth Lighting is off, entering a corner will create very odd graphical glitches like the attached image. This has the potential to be an undetectable xray, so I marked it as private. Turning on smooth lightning resolved the issue.
Environment
Ubuntu 14.04 with FOSS Xorg Nvidia Drivers, as the proprietary ones crash the game on startup
Nvidia 8400GS Geforce graphics card
Duplicate of MC-1769.