This has been happening since the nether update. I have a bed in a particular position in my large survival world, and directly below this bed is a cave. Our starter mine actually. For some reason, when I die, the bed wants to put me way down at y = 11 in this cave. I still don't know why. The bed is in a corned against two walls, so three spawn blocks are free. I think the issue has something to do with preferred spawn blocks.

Recreating this should be self explanatory.