Ixalmida

Still exists in 0.6.1. A little more detail...the lighting glitch occurs in a horizontal line that marks the division between chunks (for example, between Y-16 and Y-17 or X-16 and X-17).

I can confirm that it will happen in a 2x17 tunnel in a straight line (in the bottom two non-bedrock layers mined from end to end). Even after replacing torches to fix the lighting, after quitting and starting back up, the glitch will often reappear in the same place. With the bug, mobs manage to spawn even when spacing torches in a 6x6 grid. Haven't tried 5x5 yet.

This happens fairly regularly after I have mined out (and lighted) the bottom two non-bedrock layers from end to end, then quitting the game while still positioned in the bottom two layers (back - quit to title - back). When starting up again later, the game will usually spawn me outside the mine on whatever open area it finds above. If nighttime, this means fairly sure death as mobs are plentiful outside of my lighted house and mines. I've learned not to camp out where there's any unlighted surface above me.