This may have been patched in a more recent version but... still worth saying something about it because it is easy to reproduce

Steps to reproduce:
1.place any bed
2.set the tool to "extended vein mining"
3.break the head portion of the bed

Version (make sure you are on the latest version before reporting):

Forge: 14.23.5.2836
Mekanism: 1.12.2-9.8.2.389

I can confirm this is fixed by the rewrite I did of how the atomic disassembler breaks blocks in 1.15