Torches in mineshafts not generating correctly, often dropped or floating

The bug

Torches in mineshafts generate often dropped or without a supporting block. Most of the torches which are at valid places are attached to the naturally generated block which remained (for example stone), only a few are attached to wooden planks.

How to reproduce

1. Create a superflat world with the following preset

   3;80*minecraft:stained_glass;127;mineshaft
   

2. Use the following command

   /say @e[type=item]
   

   → You will see many torch items being listed. You can also fly around in spectator mode to see them.

How to reproduce (floating torch)

335308710995147900

3;20*minecraft:stone;3;mineshaft

/tp -1113 13 1879 180 0