If you generate Ore blocks using the material system in content tweaker and mine these ores with a pickaxe from tinkers construct, the ore block starts do drop multiple of itself. This went so far that I got whole stacks for mining a single ore.

Forge: 14.23.5.2784
CraftTweaker: 4.1.13
ContentTweaker: 4.8.0
MTLib: 3.0.5
TinkersConstruct: 2.11.0.106
Mantle: 1.3.3.39

Having similar issues on multiplayer server - don't really know how to replicate reliably, but this happens with a vanilla diamond pickaxe.

Video / Explanation
https://www.youtube.com/watch?v=hgLa-Af1uYc&feature=youtu.be

Script: https://gist.github.com/Vyraal1/49424e6de8e32644d7d4e606b9a2318e
Lines are 16 - 92

Contenttweaker - 1.12.2-4.9.1
B.A.S.E. - 1.12.2-3.11.0
Forge 2782