Torches found in abandoned mineshaft structure tunnels are floating and unattached to any nearby blocks.
Using the attached game creation settings, mineshafts found within mesa (bryce) biomes featured floating torches. I have done no testing of the issue in other world generation settings or biomes, and am unable to say if the issue persists throughout the snapshot or if it is exclusive to the settings I have used below. Two pictures have been attached demonstrating the issue.
World creation settings are as follows:
Game mode: Creative
Generate structures: ON
Allow Cheats: ON
World Type: Buffet (world generator: overworld; biome: mesa (bryce))
Bonus Chest: Off
For clarity, in creating the world, no manual entry of a world seed was used. The specific seeds used in the two attached pictures are -4074725539606775910 and -2313743621144106134
Environment
Software
Minecraft snapshot 18w16a
Microsoft Windows 10 Pro (64-bit) version 1709 (build 16299.371)
JAVA version 8 update 131 (build 1.8.0_131-b11)
Hardware
Intel Core i5-2400 3.10GHz (6MB L3 Cache)
12GB DDR3 1333MHz
AMD RADEON HD 7500 (1024MB) 675MHz core, 900MHz memory
Pardon me. While I had searched prior to this, I hadn't sorted by the date of those bug reports. My issue is already existing and is a duplicate.
https://bugs.mojang.com/browse/MC-124966 demonstrates the same issue.